Colourful London mayor Boris Johnson will wear an Australian cricket shirt for a day if the Aussies manage to win the Ashes.

Former Australian legspinner Shane Warne forced Johnson into the wager during an appearance at Lord’s to promote volunteering in the capital.

“I’ll wear an England shirt if England win the Ashes and you’ll wear an Australian shirt if Australia wins the Ashes,” Warne said on Thursday.

“We have to wear it for a day in public.”

After initially appearing reluctant to agree the mayor eventually played ball.

“It’s a deal,” he said in front of the gathered media.

“I think I’m safe.”

But Warne insists Australia are a good chance to surprise England at home.

“I think England could take Australia for granted a little bit,” he told reporters.

“They don’t fear Australia anymore and I think there is a bit of superiority with the England team especially here in England.”

The former legspinner said the Australian bowlers would be fine with James Pattinson in particular on the way to becoming “a future superstar”.

“Young (James) Faulkner I think can (also) do very, very, well,” Warne added.

The 43-year-old said there was every chance the Australian batsmen could step up too.

Captain Michael Clarke was the most in-form player in the world and Shane Watson was coming off some solid IPL form, Warne said.

David Warner had also performed well at Test level.

“Put in Chris Rogers, Brad Haddin and Matthew Wade and you’ve suddenly got some guys who can make some runs,” he said.