Anderson back into the attack but can't make the breakthrough. Two singles from the over. With the extra half-hour, there are 18 overs remaining tonight.
Drop! Tough chance. Thick edge from Pattinson off Swann, but Anderson at gully can't cling on as he throws out his right hand. Almost palmed the ball to Trott, but it goes to ground. Siddle comes down the track and smacks the ball down the ground for four to take Australia within 400 runs of victory.
Siddle takes a quick single. Tight, but home safely. Pattinson plays out the over safely enough.
Pattinson thrashes Swann through the offside for four and then whips a single to midwicket. Everyone giddy now in this crazy DRS-free zone. Siddle gets a single from the last ball of the over.
Huge lbw shout against Siddle as a full ball thuds into the pads. Broad utterly convinced, Erasmus isn't. Nor are Cook and Prior. No review, and Hawk-Eye reckons it was sliding past the leg stump. Siddle then pads up to a big reversing inswinger, and this time England do review Erasmus' not out call. Hawk-Eye says it's just clipping the off stump, so the on-field decision stands. No reviews left in this Test match.
A top-edged sweep from Siddle bounces short of Bairstow, lurking too deep at square-leg. Pattinson then plays back to a quicker ball but manages to get his bat down in time to stop the ball thudding into the pad in front of everything.
No worries for Pattinson during a Broad maiden. Time for drinks.
An edge flies just out of Anderson's reach at gully after Pattinson lunges forward against Swann. Two runs is the result. Pattinson gets off strike with a single worked behind square on the leg side and Siddle survives the remainder of the over, which includes a big attempted sweep that connects only with fresh air.
Pattinson leans into a cover drive and collects three runs from the final ball of Broad's over. Nice shot.
Single apiece for Siddle and Pattinson, both into the leg side, as Swann tosses a few tempters up above the eyeline.
Dropped! Root shells a straightforward chance after Broad finds the outside edge of Siddle's bat. Siddle escapes again when he steals a single off the last ball and Bairstow misses with his throw at the stumps - direct hit would have been out.
Pattinson joins Siddle in the middle with Australia still 421 short of their target.
Haddin departs lbw after shouldering arms to a ball from Swann - from round-the-wicket - that turned back, kept a bit low and made him look silly. Bad misjudgment, although 'Hawkeye' indicates it was spinning enough to miss leg stump. It would have been overturned on review but Australia don't have any left.
Broad is back into the attack as Cook sticks to his policy of rotating his seamers in short bursts during this innings. Haddin turns the strike over to Siddle with a single into the leg side from the first ball of the over. Siddle feels for, and misses, the next delivery, which leaves him off the seam. Broad then focuses on a shorter mode of attack but Siddle - who has a first-class hundred to his name albeit against Scotland - is equal to the task.
Swann finds Haddin's outside edge prompting oohs and aahs from the England players - but it falls safely for a single.
Siddle is surprised by some extra bounce from Bresnan and almost lobs a catch to cover, dropped just short.
Swann back on to replace Root despite his sore back. Haddin drives into the covers for a single and Siddle is off the mark with a top-edged sweep that falls safely on the leg side.
Bresnan keeps it full looking for reverse swing until the final delivery of the over, which is shorter and allows Haddin to tuck a single off his hip and retain the strike.
Siddle is the new batsman and is quickly on strike thanks to a single for Haddin off his hip. Siddle tries a sweep as Root gives it plenty of air but he doesn't make contact.
Agar had hit Bresnan for two fours through the off side earlier in the over before he was out going for another big drive. Agar was not pleased with the third umpire's decision, shaking his head on the way off - you would be hard pressed to argue there was clear evidence of an edge based on the replays/audio but 'Snicko' - which is not available as part of the DRS process - suggests it was the correct decision (even if the process to get there was wrong).
Agar is sent on his way for 16 by the third umpire after England ask for a review of umpire Erasmus' decision to turn down their caught-behind appeal. There was no mark on Agar's outside edge on the 'Hotspot' replay but third umpire Tony Hill overturns it on the basis the front-on camera angle and the sound. 'Snicko' - not part of the DRS - indicates an edge.
Haddin defends a maiden from Root in watchful fashion.
Haddin is off the mark with a single to square leg as Bresnan gets it too straight. Agar looks keen to go down swinging, slamming consecutive boundaries through the off side, the first edged just short of gully and the second right out of the middle of the bat.
Swann is on the field but man-of-the-moment Root continues for the time being. Just a bye from the over, should have been two but Haddin and Agar are understandably cautious after their mix-up in the first innings.
Bresnan finishes off the final ball of his over after tea with a dot to new batsman Agar.
Sky Bet now offering 7/2 for this match to go into a fifth day.
Yorkshire have now made 318-6 with the bat and taken 5-48 with the ball in this Test.
For an hour and a half that looked like being Australia's session. Instead it's another one for Yorkshire as Root removed both set batsmen and Bresnan picked up Smith on the stroke of tea.
Another wicket, and with it goes Australia's final review as a cross-seam delivery from Bresnan finds Smith's inside edge. Smith instantly reviews, but Hot Spot confirms a feather and England have nipped out three quick wickets after a tough session for the most part.
Think Root might be in with a chance of man of the match here.
England use a review after they think Khawaja has been caught by a juggling Trott at slip, but the ball has yet again spun straight off the pitch. Great decision by Dharmasena, and England a review down. Temporary reprieve for Khawaja, though, as two balls later the ball comes off a big edge and is quietly snaffled by Anderson at gully. Root's Ashes.
Smith calmly and relatively securely plays out a maiden over from Bresnan. Maybe three or four overs to go until tea.
Steve Smith off the mark with a single on the legside. We've had two 99-run partnerships for the fourth wicket in this Test and now a 98.
Can't keep him out of the game. Root round the wicket to Clarke, who plays the ball off the face of the bat straight into the hands of Cook at leg slip.
Bresnan into the attack in place of Anderson. Clarke clips through midwicket for two and then slashes a wide ball from Bresnan over the slips for four to bring up his half-century. Bresnan gives him another chance to free his arms outside the off stump, but this time Clarke gets a thick inside edge that very nearly cannons into the leg stump.
Big appeal for a catch at slip as Khawaja pushes forward to Root, but the ball spun straight off the pitch and missed the bat by quite a margin. Bat hitting ground made a noise which perhaps got England excited. Khawaja's already taken care of Swann and almost cleans up another key England player when his pull shot comes within inches of taking out Bell at short-leg. Nearly, but Khawaja has to settle for four runs instead.
Ball doing a bit for Anderson here, but these two set batsmen playing it quite easily now. Clarke clips the ball in the air on the legside but well short of the man on the fence.
Root replaces the injured Swann, and Khawaja works him away into the legside for two to bring up an excellent half-century. Surely too little, too late, but should cement his place for the third Test. Some classy shots and he's toughed it out against Swann.
Swann off the field at the end of that over, holding his back. Khawaja's batted beautifully, but crashing into Swann may have been his key contribution. Anderson getting the ball to reverse both ways, but Khawaja's in now and up to the task. A clip off the toes races to the midwicket boundary before a neat-looking cover-drive brings a single.
Lovely stuff from Clarke. Swann bowling round the wicket looking to bring both edges in to play, but the Australia captain skips down the track and places a drive expertly wide of mid-off for four. A clip into the legside brings a single before Khawaja heaves a short ball to midwicket for a hard-run three.
Not the best over from Anderson. Clarke defends into the offside for a sharp single before Khawaja spends the rest of the over watching the ball sail harmlessly through to Prior. One full ball outside off stump gives the batsman no problem, but does give Prior some work to do as it flies high out of the footmarks. Keeper does well to prevent any extras.
A single for Clarke from Swann's over. Good scrapping partnership this from Clarke and Khawaja. If they're still there this time tomorrow, England will be getting nervous.
Clarke gets a single from a thick outside edge and Khawaja is resolute in defence during the remainder of Anderson's over to take us through to the mid-session drinks break.
Slip, gully, silly point and short leg are crowded around Khawaja, no doubt offering plenty of pointers on how to play Swann. Khawaja collects another couple of runs as Swann drops just a touch short but also plays-and-misses at a delivery he should have been leaving well alone.
Anderson serves up a wide half volley and Clarke drives it square to the boundary to bring up Australia's 100. There is certainly reverse swing for Anderson now, he almost slips one past Clarke's inside edge with some late movement.
Khawaja's trial by spin continues. He's riding his luck in defence, not always playing with the full face of the bat but does manage to collect a couple of runs into the covers. Swann gets one to turn wildly out of the rough but the line was too wide to draw a shot.
Anderson is back into the attack and Clarke edges his first ball down to the third-man boundary, it was always under control. Anderson generates some reverse swing later in the over, getting it to tail back at Australia's captain.
Clarke works a single into the leg side from the first ball of Swann's over, bringing Khawaja onto strike. Swann has plenty of rough to aim at outside the left-hander's off stump, it's a very tricky assignment for the batsman. Swann beats the outside edge with one delivery that Khawaja opts to play back to.
Broad switches to round-the-wicket and much fuller against Khawaja, who fails to beat the infield with a couple of attractive drives.
Clarke is not willing to allow Swann dictate matters and dances down the pitch to lift a four back over the bowler's head. Fine shot.
Broad's plan to Clarke is short in an effort to expose any lingering back problems Australia's skipper may be suffering from. It is hostile stuff from Broad and Clarke is hit on the badge of the helmet after taking his eye off one. Clarke ends the over with a less-than-convincing pull for a single, which also completes the 50 partnership with Khawaja for Australia's fourth wicket from 93 balls.
It's the extra pace and bounce in this Lord's pitch that Swann is enjoying compared to Trent Bridge last week. Clarke turns a single to midwicket. The final ball of the over turns lavishly out of the rough and the left-handed Khawaja, playing forward defensively, is not close to getting an edge.
Khawaja tucks into another short delivery from Broad, this time getting his pull just in front of square. Khawaja's quite a stylish player, wristy, and that's the third time he's done that to Broad since lunch.
Khawaja is looking a little bit more comfortable against Swann now, picking up five runs from the over, including a three to third-man from a full toss.
Broad pulls his length back but Khawaja looks a good player of the short ball, rocking back to roll his wrists on a pull that races away to the boundary. Khawaja, who plays his state cricket for Queensland these days after starting out with New South Wales, gets off strike with a single into the leg side. Clarke leaves the final ball of the over and is struck on the pad after it veers back appreciably off the pitch. Broad appeals for lbw but it was much too high.
Swann drops just a touch short, allowing Khawaja to go back and turn it to midwicket for three runs.
Decent pace and bounce for Broad from the Pavilion End. Clarke wears one in the chest - ouch. Clarke collects two off his pads to finish the over. Australia require another 516 for victory.
Another eventful over from Swann includes some ropey defence from Khawaja, a collision between batsman and bowler during a quick single (Khawaja had his head down and barged into Swann's back with his shoulder. The England bowler was briefly writhing around on the floor but he is soon up on his feet and appears fine) and Clarke dancing down to loft a drive over the infield - only just - for four.
The sun has burnt away with the morning clouds leaving us with a blue sky above Lord's for the start of the afternoon session. Runs for Khawaja as Broad's over disappears for 10, including two boundaries, the first edged down and through the packed slip cordon to third man and the second pulled behind square.
Another session goes England's way. The Joe Root double-century bid may have failed, but since then it's been all England, and all so predictable. Watson lbw to a seamer, Swann picking up a pair of left-handers. Hard to see Australia's route out of this one.
Swann rips one past Khawaja's outside edge but then starts one too straight and allows the left-hander to escape the strike with a clip into the legside. Clarke blocks the last two balls of the session.
Couple of twos for Clarke, the first runs Bresnan has conceded, via a clip through midwicket and a controlled steer to third-man.
Lovely shot from Clarke, nimble footwork getting him to the pitch and allowing him to drive Swann through the covers for four. A tuck off his pads brings a single, and Khawaja sees out the rest of the over safely enough.
Maiden over from Bresnan. Australia have done one thing right here: Khawaja has faced only one ball from Swann.
Missed stumping! Clarke using his feet to Swann but beaten on the outside edge after playing for turn. Luckily for the Australia captain, Prior was also playing for turn and the ball hits his right shin and bounces away to safety.
Superb over from Bresnan, rapping Khawaja on the gloves with one that bounces off a length and then snaking two deliveries past the outside edge.
Clarke, who should really be batting at four, is in at five. He's immediately using his feet against Swann. Picks up two with a clip to fine-leg.
Another lbw, and this time there is a review. Doesn't do Hughes any good, though, with Hawk-Eye showing that a straight-onner from Swann would've hit the leg stump had the left-hander's pad not got in the way.
Hughes looking solid in defence against Bresnan here. Migh think about coming round the wicket.
Better from Hughes, getting well forward to smother Swann and then getting right back to knock the last ball of the over into the legside for a single.
Khawaja plays out a maiden from Tim Bresnan. Genuine case for getting Root on against this pair of southpaws.
Swann bowling into these craters against Hughes and Khawaja must come pretty close to cruel and unusual. Tough test for Matt Prior, too, who can't get gloves to a spinning, bouncing ball and gives up two byes.
Maiden over from Anderson to Khawaja. Time for episode two of the Swann Show.
One left-hander departs, another arrives. Phil Hughes the new man. Swann could enjoy himself here.
At least this one pitched. Rogers spooked by a ball that spins sharply out of the rough then shoulders arms to one that goes straight on and knocks back the off stump.
Here's Swanny...
Nice shot from Khawaja, clipping a full delivery from Anderson off his toes through midwicket for four. A shorter ball is tucked away for a single. Don't think it'll be too long before we see Swann bowling into the craters against these left-handers. Rogers nudges to leg for another single.
Rogers turns a single into the leg side off Broad and Khawaja follows suit to get off the mark and retain the strike.
That was masterful bowling from Anderson, exploiting Watson's planted front foot. New batsman Khawaja plays defensively at the final two balls of the over.
History repeats itself as Watson goes lbw for the third time in a row. It was a good delivery from Anderson that came back off the pitch. The only change this time is that Watson walks off without reviewing it.
Rogers is beaten outside off stump by a good delivery from Broad that slanted across the left-hander and caught him playing from the crease. Rogers turns a single into the leg side later in the over and Watson is text book in defence to the final ball.
Watson continues to ride his luck against Anderson. He makes no contact after chasing a drive well outside off stump and then skews another drive through backward point. Anderson drifts onto leg stump and Watson helps it on the way to the vacant fine-leg for four. Watson appears to have moved his guard slightly further to the leg side in response to his lbw dismissals in the first innings here and second innings last week at Trent Bridge.
Watson cuts hard and into the ground after being offered some width outside off stump by Broad. Bairstow parries at backward point to keep it down to a single. Rogers gets off the mark to his 10th ball faced with a check drive for two through mid-off. Huge contrast in the way these two openers go about their work, the right-handed Watson planting his front foot and looking for big shots through the off side and the shorter, left-handed Rogers leaving as much as possible and defending with a compact technique.
Watson pushes a single through the backward point region and Rogers plays defensively during the remainder of Anderson's over. There are around 173 overs left in the match (can't be exact on that as it depends on how quick England's over-rate is today).
Broad takes the first over from the Nursery End. Watson is too early on a drive but follows through anyway and lofts it over extra cover for three. Replays showed that delivery went through the top of the pitch and produced an explosion of dust, making driving on the up a dangerous game.
Watson reduces Australia's requirement to 579 with a think edge to James Anderson's second delivery that drops just short of gully and runs away to the boundary. Good start from Anderson, passing Watson's outside edge later in the over with a ball that swung in the air and seamed off the pitch. Watson gets off strike with an inside-edged drive out to square-leg for a single.
Root's exit prompts England to declare their second innings at 349-7, leaving Australia to chase a target of 583 to level the series.
With nine fielders back on the boundary, Root's quest for a double ton ends when his attempted 'ramp' goes high in the air to Smith at third-man. An ugly end to an excellent innings of 180 from the 22-year-old that spanned 338 balls and included 18 fours and two sixes.
Dropped! Prior pushes a drive straight back at Agar but the bowler just doesn't pick it up. Would have been an easy catch. Four byes to end the over after Prior misses with a sweep.
Bairstow's downfall was due to him trying to cut a ball that was too close to his body. New batsman Matt Prior is off the mark with a single run down to third-man to again keep Root away from the strike, which is a clear tactic from Australia this morning.
Harris get the breakthrough in the third over of the day, finding Bairstow's outside edge two deliveries after going past it. Wicketkeeper Haddin does the rest.
Left-arm spinner Agar aims at the rough outside the right-hander's leg stump. Bairstow skips down the pitch and lofts a six back over the bowler's head. Australia are happy to give Bairstow a single from the final ball of the over again, presumably on the basis that the longer Root needs to get his double century, the less time they will have to bat out for a draw.
Root starts with a single into the leg side from a back-foot defence. Gentle start from Harris, Bairstow keeping the strike with a single of his own to midwicket.
Glenn McGrath rings the bell to indicate five minutes until the start of play and the players soon make their way to the middle. There is one early surprise; no England haven't declared but Australia are going to give Harris the first over - still with the old ball - instead of wrapping him in cotton wool.
This is Nasser Hussain's summation of the options available to England skipper Alastair Cook today: "Declare now - you'll win. Declare after 40 minutes - you'll win. Declare at lunch - you'll win."
There is a bit of cloud cover at Lord's this morning, could encourage swing early on. The sun is due out as the day progresses. The pitch looks to be holding together well, given the hot weather and the fact this is now day four of the match. There is some rough for the spinners to aim at and Ashton Agar did get a couple to turn and bounce alarmingly yesterday, so Graeme Swann will certainly be a handful when England eventually have a bowl.
Australia bowled their spinners in tandem last night and did not take the second new ball, in effect raising the white flag. It will be interesting to see what approach they take this morning, should they take the new ball and let Siddle and Pattinson have a burst with it (Harris and Watson are unlikely to bowl, Harris to save his fragile body for later in the series and Watson because he's going to have to open the innings at some point).
No suggestion that England will declare overnight as Root will have his eyes on a double century. That is 22 runs away for the Yorkshireman so, if he gets there, England's lead will be approaching 600, which could prompt a declaration. But Alastair Cook and Andy Flower are both small c conservatives and therefore England might well press on further and then have a burst either side of lunch with the new ball.
Welcome to our coverage of day four of the second Ashes Test at Lord's. England are due to resume on 333-5 in their second innings, a lead of 566, with Joe Root on 178. Play starts at 11am (BST).