Around a dozen British Conservative MPs will formally throw their hats into the ring on Monday in the fight to replace Theresa May as party leader and Prime Minister, with her former foreign secretary Boris Johnson seen as the runaway favourite.

Nominations to succeed May, who resigned on Friday as head of the ruling Tory party following her failure to deliver Brexit, opens at 10:00am (0900 GMT) and closes at 5:00pm (1600 GMT).

Britain’s departure from the European Union, twice delayed and now set for October 31, will dominate a contest scheduled to run until late July and which, in the past, has been characterised by shocks and surprises.

The new leader of the centre-right party, which won the most seats at the last general election in 2017, will almost certainly become Prime Minister, with May remaining in Downing Street in the meantime.

Unofficial campaigning already started weeks ago and Johnson has emerged as the undisputed frontrunner – although in previous leadership races the early pacesetter has never been victorious.

Current Foreign Secretary Jeremy Hunt, Interior Minister Sajid Javid, and Environment Secretary Michael Gove are perhaps the best-known names of 10 other MPs also in the running.

Each candidate must be nominated by at least eight Conservative MPs.

In a series of ballots over the coming weeks, party lawmakers will then whittle down the list of names to just two.

The final choice will then be made by more than 160 000 paying party members.

“The obvious big issue is Brexit – there is very little else that preoccupies the Conservative Party at the moment,” Tim Bale, politics professor at Queen Mary, University of London, told AFP.

“Boris Johnson is likely to win this election because he is offering the Conservative party members what they want… a no-deal Brexit,” he added, referring to Britain leaving the EU without a formal agreement.

But “whether he can actually achieve that is another matter,” the expert said.

Johnson, 54, a former mayor of London and key figure in the divisive 2016 EU referendum campaign, served as May’s foreign secretary until he resigned last summer over her Brexit strategy.

Charismatic and popular among grassroots Conservatives, he is less liked by Conservative MPs sceptical of his bombastic style and chequered track record.

Although some believe his undistinguished two-year tenure as Britain’s top diplomat may work against him, Johnson has garnered growing support from cabinet members and both centrist and right-wing Tories.

He has vowed Britain will leave the EU “deal or no deal” in October and said this weekend he would withhold the country’s Brexit bill if the EU does not offer improved withdrawal terms.

Johnson also argued only he could defeat leftist Labour leader Jeremy Corbyn and anti-EU populist Nigel Farage, whose new Brexit Party has been poaching Tory voters disgruntled at the party’s handling of Brexit.

Johnson’s closest rival is seen as Environment Secretary Michael Gove, a eurosceptic who also fronted the 2016 Leave campaign.

He turned on Johnson during the last leadership contest in 2016, in a move that ultimately cleared the path for May.

However, the 51-year-old has become mired in controversy after he admitted, with deep regret, to using cocaine on several occasions two decades ago.

In contrast to Johnson on Brexit, Gove has said he would delay leaving the EU by “a few extra days or weeks” if needed to seal a new deal.

Another leading contender, Hunt, has vowed to renegotiate the agreement May struck with Brussels, claiming Sunday that he had received encouraging signals for such a move from German Chancellor Angela Merkel.

All of the candidates will take part in a series of private hustings in front of MPs, and some have also committed to appear in television debates.

Once selected, the two finalists will then hold at least a dozen party member events around Britain.

The other contenders are regarded more as long shots.

Ex-Brexit Secretary Dominic Raab, 2016 leadership contender Angela Leadsom and former Work and Pensions Minister Ester McVey are all ardent eurosceptics who insist on Britain leaving the EU in October.

Among those taking a more moderate stand on Brexit are International Development Secretary Rory Stewart, Health Minister Matt Hancock, former chief whip Mark Harper and former universities’ secretary Sam Gyimah, who backs a second referendum.