Home Secretary Theresa May, who backed staying in the EU, has also entered the contest. Nominations close at noon. The winner of the contest is set to be announced on 9 September.

Mr Johnson, the former mayor of London, is widely expected to enter the race with a speech later, and to place Brexit at the heart of his "optimistic vision" for the country. He is expected to say the greater self-determination that leaving the EU will bring is an opportunity to "believe in ourselves and the values of our country". Energy minister and Brexit campaigner Andrea Leadsom has also thrown her hat in to the ring, joining former Defense Secretary Liam Fox and Work and Pensions Secretary Stephen Crabb among the runners and riders.

Mr Gove's announcement that he will challenge the leadership was unexpected, as the justice secretary had been expected to throw his weight behind fellow leading Leave campaigner Mr Johnson for Conservative leader. Explaining his decision, he said: "I have repeatedly said that I do not want to be prime minister. That has always been my view. But events since last Thursday have weighed heavily with me.

"I respect and admire all the candidates running for the leadership. In particular, I wanted to help build a team behind Boris Johnson so that a politician who argued for leaving the European Union could lead us to a better future. "But I have come, reluctantly, to the conclusion that Boris cannot provide the leadership or build the team for the task ahead."

Setting out his pitch for the leadership, the cabinet minister - who was formerly the education secretary - said: "I want there to be an open and positive debate about the path the country will now take. "Whatever the verdict of that debate I will respect it. In the next few days I will lay out my plan for the United Kingdom which I hope can provide unity and change."

Mr Gove said the British public, in voting to leave the EU by 52% to 48%, last week, "rejected politics as usual and government as usual" and wanted "a new approach to running this country". The UK faced "huge challenges" but also "huge opportunities", he said, and added: "If we are to make the most of the opportunities ahead we need a bold break with the past."

An additional information to be provided about Mr. Gove. Unlike Mr Johnson, the 48-year-old has gone out of his way in the past to put a limit on his personal ambitions, even going so far as to suggest that he was not equipped to do the job of prime minister.

The former Times journalist, who entered Parliament in 2005, has been a close personal friend of David Cameron and George Osborne and was a key figure in the party's modernization that led to its return to power in 2010.
He subsequently became a reforming, if controversial, education secretary and is regarded as one of the party's intellectual heavyweights.

The justice secretary's decision to back the Leave side was one of the key turning points in the campaign and although it is said to have strained his relations with Mr Cameron, he is still respected on both the Remain and Leave wings of the party and is likely to be a pivotal figure in the coming months.