Combo group of ten file photos showing the contenders in the Conservative Party leadership race, with top row from left, Boris Johnson, Dominic Raab, Jeremy Hunt, Rory Stewart, Mark Harper, and bottom row from left, Esther McVey, Matt Hancock, Andrea Leadsom, Michael Gove, Sajid Javid.
Gove apologised but critics accused him of hypocrisy, noting that, in a previous role as education minister, he had signed off on rules to ban teachers for life for taking cocaine.
Whereas candidates in the past needed just two lawmakers supporting them, the Tory party's influential 1922 Committee - which conducts the election process - made a decision to change the rules earlier this month in a bid to speed up the contest, requiring a minimum of eight MPs for each candidate.
Global development minister Rory Stewart has been holding conversations with the public over the past few days as part of his strategy, with former ministers Andrea Leadsom and Esther McVey among some of the other key contenders. In votes starting Thursday, Conservative lawmakers will narrow the field down to two, who will be put to a vote of party members nationwide.
Mr. Johnson is expected to launch his campaign on Tuesday and so far he has kept a lower profile than the other candidates.
It's just another measure of how odd a contest is under way to be Prime Minister that a politician likely to make the divisions besetting Britain even worse than they already are is seen as the best option by those who might give him the job.
He said he would seek a new Brexit deal and could not promise the exit would happen by October 31.
He has also tried to appeal to the British middle class by promising to cut taxes for people who earn more than €56,000 a year in a move set to cost Britain's treasury about €11bn a year.
Former foreign minister Johnson is the bookmakers' clear favourite to succeed May and, according to polls, the most popular with the 160,000 party members who will ultimately make the choice.More news: Sri Lanka president vows to block Easter attacks probe
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"It wasn't enough to believe in Brexit - you've got to be able to deliver it".
"That isn't credible by October 31 and there won't be a majority in Parliament to let us leave without a deal".
"Scottish taxpayers now face the prospect of paying for a tax cut for the likes of Boris Johnson and his cronies", said MSP Angela Constance.
Mr. Gove's campaign got off to a rough start on Monday after he admitted using cocaine several times when he worked as a journalist more than 20 years ago.
Media captionDominic Raab: "I am the candidate who can be trusted to deliver on Brexit". It "it "probably tells you that I was doing my job in terms of pressing them hard and making sure that Britain's interests were resolutely defended", he said".
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.
For his part, Jean-Claude Piris, the former top lawyer of the EU Council in Brussels, summed up the mood in the EU capital when he told British newspaper the Guardian: "People in Brussels are fed up that the political class in the United Kingdom has gone a little bit crazy".
The differences between the candidates reflect the Conservative disunity on the issue, which has meant that, three years after the United Kingdom voted by 52 per cent to 48 per cent to quit the European Union, it remains unclear how, when or even whether it will leave.
Johnson's threat on the divorce bill was "a matter of respecting global law", she also said.