US Secretary of State John Kerry said on Tuesday that Britain’s vote to leave the European Union might never be implemented and that London is in no hurry to go.

US Secretary of State John Kerry said on Tuesday that Britain's vote to leave the European Union might never be implemented and that London is in no hurry to go.

Speaking one day after talks with Prime Minister David Cameron, Kerry said the outgoing British leader feels "powerless" to negotiate a departure he does not want.

"This is a very complicated divorce," Kerry told the Aspen Ideas Festival, referring to Britain's negotiated exit from the EU after last week's "Brexit" referendum.

Kerry, who visited Downing Street on Monday, said Cameron was loath to invoke "Article 50" of the Lisbon treaty, which would trigger a two-year timetable for departure.

London, Kerry explained, does not want to find itself boxed in after two years without a new association agreement and to be forced out of the EU without one.

Cameron "feels powerless -- and I think this is a fair conclusion -- to go out and start negotiating a thing that he doesn't believe in and he has no idea how he would do it, the top US diplomat said.

"And by the way, nor do most of the people who voted to do it," Kerry said, apparently referring to "Leave" campaigners such as former London mayor Boris Johnson, now the frontrunner to replace Cameron as premier.

Asked by the panel moderator if this meant the Brexit decision could be "walked back" and if so how, Kerry said: "I think there are a number of ways."

"I don't as secretary of state want to throw them out today. I think that would be a mistake. But there are a number of ways," he said.