Nigel Evans, executive secretary of the 1922 Committee, warned the field could swell to as many as 20 as Mark Harper, the former chief whip, announced his intention to stand.
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Welcome to The Independent's politics liveblog where we will be bringing you all the updates from Westminster - and the ongoing race to succeed Theresa May in Downing Street.
The former chief whip Mark Harper has become the 12th candidate to enter the Tory leadership race, claiming he offers “fresh thinking”.
He joins Boris Johnson, Dominic Raab, Michael Gove, Jeremy Hunt, Rory Stewart, Esther McVey, Sajid Javid, Andrea Leadsom, Matt Hancock, Kit Malthouse and James Cleverly.
So where do they all stand on Brexit?
Boris Johnson, the favourite to succeed Theresa May, has vowed to take Britain out of the EU on October 31, "deal or no deal".
Dominic Raab, the former Brexit secretary, has said he would prefer to leave the EU with a deal, but added that the UK must "calmly demonstrate unflinching resolve to leave in October - at the latest".
Jeremy Hunt, the foreign secretary, voted Remain in 2016 and appears to be in favour of leaving the EU with a deal. "Doing deals is my bread and butter as someone who has set up their own business," he said.
Rory Stewart, the international development secretary, also wants a deal. He says a no-deal Brexit would be "a huge mistake, damaging, unnecessary, and I think also dishonest".
Esther McVey, the former work and pensions secretary, says the UK should be prepared to leave the EU with no deal. "We must now leave the EU on October 31 with a clean break," she said.
Matt Hancock, the health minister, says he would take a different approach to the one Theresa May used in order to get Commons support for a Brexit deal. He told the BBC that a no-deal Brexit "simply won't be allowed by Parliament".
Andrea Leadsom, former leader of the House of Commons, says that if she was PM the UK would quit the EU in October with or without a deal.
Michael Gove, the environment secretary, says he is "ready to deliver Brexit" but has so far avoided the question of whether he would be prepared to lead the UK out of the EU without a deal.
Sajid Javid, the home secretary, backed Remain in the referendum but has since positioned himself as a firm Leaver. He says his party "must get on and deliver Brexit".
Kit Malthouse, the housing minister, is best known for attempting to bring Leavers and Remainers together for the so-called "Malthouse Compromise" on Theresa May's withdrawal agreement. It seeks to replace the backstop with "alternative arrangements".
James Cleverly says be believes "the case for Brexit is still valid" but claims that leaving without a deal is "not his preferred choice".
Mark Harper backed Remain in the referendum but claims he has the best chance of solving Brexit because he did not serve in the government that failed to deliver a deal.
QUB Conservatives on Twitter“Great day out meeting Her Majesty’s Home Secretary Sajid Javid MP. He delivered a very interesting speech which addressed how the United Kingdom will leave the European Union and do so with an agreed deal. @sajidjavid @NIConservative @RowanWise1 @Aaron_Rankin87 @Conservatives”
Iain Duncan Smith, the former Tory leader, has compared the large number of candidates to the "Charge of the Light Brigade".
He was one of only five candidates to stand in the 2001 leadership contest, beating Ken Clarke in the members ballot after Michael Portillo, David Davis and Michael Ancram were eliminated.
Mr Duncan Smith said the swollen field had left the Conservative Party "looking like chaos" and urged the 1922 Committee to look at the rules which allowed MPs to stand with only two backers.
Meanwhile Jeremy Corbyn is facing increasing pressure to clarify Labour Party policy on Brexit following the disappointing European election results.
Alastair Campbell, the former spin doctor, said Labour could be wiped out unless it backed a Final Say, and risked ushering Boris Johnson into Downing Street and paving the way for a no-deal Brexit.
Here's our report from political correspondent Lizzy Buchan.
The Liberal Democrats, on the other hand, are riding high as a new poll suggests it has become the most popular party in the country, with 24 per cent.
The Lib Dems are also staging a leadership contest, as Vince Cable is due to stand down on 23 July.
Jo Swinson and Sir Ed Davey are both in the running for the job.
That poll - which showed the Brexit Party in second with 22 per cent - has been described by Nigel Farage as "an establishment attempt to suppress the truth".
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