THE battle for the Conservative leadership has been dramatically transformed after Boris Johnson announced that he will not stand in the race to succeed David Cameron.

The former London mayor's decision not to join the battle leaves Home Secretary Theresa May as hot favourite to be the next Prime Minister.

It came after the shock announcement by fellow Brexit campaigner Michael Gove - who had widely been expected to be Mr Johnson's running mate - that he was putting himself forward for the leadership.

In a dramatic press conference just moments before the deadline for nominations passed, Mr Johnson said that the next Tory leader would have to unify his party and ensure that Britain stood tall in the world.

And he said: "Having consulted colleagues and in view of the circumstances in Parliament, I have concluded that person cannot be me."

Mr Johnson's withdrawal from the fight before battle had been joined came after Justice Secretary Mr Gove - who campaigned alongside Mr Johnson for Leave in the EU referendum - said the former London mayor "cannot provide the leadership or build the team for the task ahead".

In a bombshell announcement released just hours before Mr Johnson was due to formally launch his leadership bid, Mr Gove said he had "reluctantly" concluded that he could not support the ex-London mayor.

"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," he said.

"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. I have, therefore, decided to put my name forward for the leadership."

Mr Johnson made supporters and journalists wait until the end of his speech before revealing his intentions, just moments before the official announcement from the Tories 1922 Committee that there would be five candidates in the contest - Mr Gove, Mrs May, Work and Pensions Secretary Stephen Crabb, former defence secretary Liam Fox and pro-Brexit energy minister Andrea Leadsom.

Britain had a chance "to think globally again, to lift our eyes to the horizon, to bring our uniquely British voice and values, powerful, humane, progressive, to the great global forums without being elbowed aside by a supranational body" and the agenda for the next PM would be to " seize this chance and make this our moment to stand tall in the world", said Mr Johnson.

But he added: " I must tell you, my friends, you who have waited faithfully for the punchline of this speech, that having consulted colleagues, and in view of the circumstances in Parliament, I have concluded that person cannot be me.

"My role will be to give every possible support to the next Conservative administration, make sure we properly fulfil the mandate of the people that was delivered at the referendum and to champion the agenda I believe in."

Meanwhile, Mrs May launched her bid for Number 10 with a message that the country needed "strong leadership" at a time of economic and political uncertainty and - in a clear swipe at Mr Johnson - warned that politics was not a "game". Contrasting herself with those who enter politics out of "ideological fervour" or "ambition or glory", she said she was a "public service" politician who was not "showy" but could "get the job done".

"If you are from an ordinary working class family, life is just much harder than many people in politics realise," she said.

"Frankly, not everybody in Westminster understands what it's like to live like this and some need to be told that it isn't a game. It's a serious business that has real consequences for people's lives."

Mrs May - who was a low-key supporter of Remain during the referendum - made clear she will not attempt to back away from last week's vote to leave the EU, saying: "Brexit means Brexit."

In a further olive branch to Leave supporters, she said she would create a new Government department, headed by a Cabinet-level minister who had campaigned for Leave, to oversee the UK's departure from the EU.

Signs of the tensions that had developed between Mr Johnson and Mr Gove were exposed when an email from the Justice Secretary's wife was accidentally sent to the wrong person.

In it, journalist Sarah Vine warned her husband that he must secure a specific guarantee about his future before making any deal with the former London mayor and should "not concede any ground".

In a further fracturing of the Vote Leave campaign, Mrs Leadsom announced she was making her own bid for the leadership while the Leader of the Commons Chris Grayling has come out for Mrs May.

Cabinet ministers Nicky Morgan and Jeremy Hunt both ruled out leadership bids, with Mrs Morgan backing Mr Gove and Mr Hunt backing Mrs May.

Justice Minister Dominic Raab, a Gove ally who backed the joint ticket and who penned a newspaper article which appeared this morning backing Mr Johnson as PM, said the ex-London mayor's "cavalier" attitude had scuppered the plan.

The party needed a "unity figure who can bring people together and ultimately put a team together", he told Sky News.

"Until the 11th hour Michael Gove was committed to doing that with Boris. It hasn't happened and some of the reassurances that we had had about turning a dream ticket into a dream team didn't materialise."

Liberal Democrat leader Tim Farron said: "Boris follows the Bullingdon playbook: you break it and someone else has to fix it."

Mr Gove announced his decision to a small group of MPs gathered in his office just after 9am.

Culture Minister Ed Vaizey, who was among the group, said they had all been "stunned" at the news.

"It is pretty clear that he was ready to back Boris but the closer it got, the more he thought he was not the right person," he said.

"Michael's logic is that he doesn't think Boris can do it so he should step up to the plate."

The chairman of the 1922 Committee, Graham Brady, announced that the first set of voting will take place on Tuesday as the party's MPs winnow down the field of five candidates to two.

With the least successful contender eliminated at each round, further ballots will be held on Thursday, then successive Tuesdays and Thursdays until two front-runners emerge to be put forward to the party membership in the country for a final decision. Mr Brady said the committee wants a winner to be chosen by September 9.

A handful of Tory MPs reacted with disbelief as news that Mr Johnson would not be seeking the leadership filtered through as they waited for Mr Brady's announcement.

Former international development secretary Andrew Mitchell said he had not expected Mr Johnson to withdraw, telling the Press Association: "I thought Boris was going to launch his campaign but his numbers were haemorrhaging so he decided to make the obvious decision."

He warned the candidates to treat the leadership race seriously: "It's jolly good theatre but this is not the contest for the president of the Oxford Union, it's the decision about our next prime minister on what is probably the most difficult wicket any time since 1940."

He added that it was "not impossible but quite difficult" for anyone who campaigned to remain in the European Union to become prime minister.