Boris Johnson says 'of course' he will run to replace May as soon as she quits as prime minister

Brexit figurehead Boris Johnson has said that "of course" he will run for the Conservative leadership when a vacancy becomes available.

The former foreign secretary, who was speaking at an insurance conference in Manchester, is the first Tory big-hitter to declare his intention to fight to be Prime Minister.

Asked by broadcaster Huw Edwards in an on-stage interview whether he would stand if a vacancy was available, Johnson replied: "Of course I'm going to go for it."

He stressed that there was currently no vacancy, but his comments will be taken as confirmation that he intends to fight to become Prime Minister when Theresa May stands down.

Mr Johnson's ambition to replace Mrs May has long been Westminster's worst-kept secret.

He has long led popularity contests among Conservative activists and his high profile personality is viewed by many as a potentially decisive factor in keeping Tories in power at the next election.

But his elevation would be fiercely resisted by Remain forces in the upper echelons of the party, who fear he would take the UK out of the European Union without a deal.

The next Tory leader will be chosen in a ballot of the party's approximately 125,000 members around the country.

But to get onto the ballot paper, Mr Johnson would have to make a shortlist of two chosen by MPs in a voting process to whittle down what is expected to be a large field of contenders.

Other senior figures believed to be limbering up for a possible bid include Mr Johnson's successor as Foreign Secretary Jeremy Hunt, as well as Home Secretary Sajid Javid and Health Secretary Matt Hancock. Mr Johnson may also face competition for the Leave-backing vote from former Brexit Secretary Dominic Raab.

Public declarations have so far been made only by International Development Secretary Rory Stewart, Leader of the Commons Andrea Leadsom and former minister Esther McVey, all seen as relative outsiders in the race to succeed Ms May.

Ms May has said she will stand down as Conservative leader once her Brexit deal is ratified, handing over to a new leader to take on negotiations over the UK's future relations with the EU.

But she is believed to be resisting demands from grandees on the backbench 1922 Committee to set out a timetable for her departure if the Withdrawal Agreement Bill is defeated in a series of votes due to begin early next month.

Expectations of a Johnson bid have been fuelled by reports of private meetings with MPs to sound out possible support, as well as a sudden spate of visits to constituency associations.

Mr Johnson was widely credited with tipping the balance in favour of Leave in the 2016 EU referendum, but became a magnet for controversy for his oft-repeated claim - branding misleading by statistics watchdogs - that the UK hands over £350 million a week to the EU.

He walked out of the Cabinet in July last year in protest at Ms May's Chequers plan for Brexit, which he branded "woeful".