England will be "incredibly tough" to beat in this summer's Ashes series, according to Brendon McCullum.
The New Zealand captain is in perfect position to judge the current state of England's Test team having gone head-to-head with Alastair Cook five times in the past four months.
It took a rearguard action in Auckland to earn England a 0-0 series draw in March, but New Zealand were twice steamrolled earlier this summer in a one-sided rematch.
And McCullum, who oversaw a 247-run defeat in the second Test at Headingley, does not foresee Australia faring much better than the Kiwis.
He said: "I think England are going to be a tough team to beat. They seem to have got their swagger back against us in that final Test match.
"What we saw in that Test match is a team that when they are firing they are an incredibly tough team, not just to beat but to compete against.
"I thought for long periods of the summer we held our own against them but when it really mattered they flexed their muscles. I don't expect that will change in the home summer here against Australia."
McCullum also offered support for Nick Compton, the opener who twice scored hundreds in New Zealand but now looks set to lose out to Joe Root after scoring just 39 runs in four innings on home soil.
"It's probably a touch harsh," he said. "For us we came off a Test series where he performed exceptionally well against us.
"We targeted him as one of the key wickets at the top of the order. He pained us for a fair amount of time back home with his innings.
"I thought we bowled exceptionally well to him in England. They weren't easy batting conditions either at the top of the order."