Stephen Ferris knows Ireland must be at their best to trouble England at Twickenham next Saturday.
The rivals meet in the climax to the 2012 RBS 6 Nations in a contest that is likely to determine who finishes second behind Wales.
England can still claim the title but need France to beat Wales in Cardiff earlier in the day and make up a points difference of 38.
The Irish warmed up for their trip to London by thumping winless Scotland 32-14, but Ferris accepts Stuart Lancaster's side will provide far stiffer opposition.
"I've been fortunate to win with Ireland at Twickenham and I know that you have to be on top of your game to get a result," the Ulster flanker said.
"We are improving week on week and are happy with our set-piece, but we know England are strong there.
"They won't concede any soft tries, like Scotland did, either.
"We have to chase the box-kicks down hard and get behind them. Rob Kearney is going to be busy in the air again."
Ferris was in fine form once more, producing a string of big tackles against Scotland in a typically aggressive defensive shift, and is pleased with the improvements the team have made in that department.
"In the last couple of weeks I've done a bit more defending than I would have liked but that's the way it goes," the 26-year-old said.
"I've put my body on the line and got into the defensive line, reading it well.
"Overall we defended well and apart from that soft try Scotland didn't look like breaking us down.
"Since the criticism we took after the Wales game we've defended pretty well. We've worked hard on it.
"Personally and as a team I felt we have improved defensively."
Ferris was delighted by the performances of Munster duo Donnacha Ryan and Peter O'Mahony, who replaced the injured Paul O'Connell and Sean O'Brien against Scotland.
"Donnacha came in and took over the lineout, he had an awesome game. He's very calm and cool, nothing seems to faze him," he said.
"Peter was great. There's a bright future for him. He likes to get stuck in. He's typical Munster - as hard as nails."