Boris Johnson will not stand for Conservative leader, he has announced.

In a surprise announcement, the former Mayor of London said he would “support” the next Tory leader but that it would “not be me”.

Mr Johnson gathered the media for a speech at a central London location for what was expected to be his campaign launch.

However, after giving a speech outlining his view that the next Prime Minister should champion the "forgotten" people in Britain, he ruled himself out for the top job.

“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," he said.

“My role will be to give every possible support to the next Conservative administration to make sure that we properly fulfill the mandate of the people that was delivered at the referendum, and to champion the agenda I believe in – to stick up for the forgotten people in this country.”

Mr Johnson has long been the favourite to suceed David Cameron, who stepped down after being defeated in the European Union referendum.

However his campaign was dealt a fatal blow this morning after his former Vote Leave ally Michael Gove announced that he was standing as leader.

In his announcement speech Mr Gove said he did not believe Mr Johnson could be trusted to unite the Conservative party and lead the country.

Asked about Mr Gove's decision, Mr Johnson's father Stanley Johnson quoted Caesar's supposed last words after he was stabbed by his former friend Brutus.

"'Et tu Brute' is my comment on that," he told BBC Radio 4's The World at One. "I don't think he is called Brutus, but you never know."

The favourites in the Tory leadership race Show all 5 1 /5 The favourites in the Tory leadership race The favourites in the Tory leadership race Theresa May The longest-serving Home Secretary in 100 years took a back seat in the referendum campaign. While backing Remain, she did not hit the campaign trail and delivered only a handful of speeches and interviews, and was critical of many aspects of the EU, particularly the European Convention on Human Rights. Hedging her bets allows her to now emerge as a ‘unity’ candidate, and she is said to have been building up her back-room staff in preparation for a leadership bid. She has the significant advantage of having served in one of the great offices of state, in a steady and competent manner that has won her many admirers within party and the civil service. At a time of great instability, it may be that she is viewed as steady hand on the tiller. Mrs May does however, lack the ‘star quality’ of a Boris Johnson and party members may doubt her ability to connect with ordinary voters PA The favourites in the Tory leadership race Michael Gove The Justice Secretary may be able to set himself up as ‘the thinking Tory’s Brexit candidate’. Made an enormous political and personal decision to back Leave, taking on his old friend David Cameron. He performed well during the TV debates, and will be an admired figure among Eurosceptic Conservatives. Along with Johnson, he will be hindered by the fact that he led a very divisive campaign, characterised by ‘blue-on-blue’ action. MPs may also judge that he lacks Boris Johnson’s wider appeal with the electorate. Possibly more likely that he will settle for being his new bosom buddy Boris’s Chancellor Getty The favourites in the Tory leadership race Stephen Crabb Highly-rated Work and Pensions Secretary, raised on a council estate, so could reach out to non-traditional working class Tory voters Getty Images The favourites in the Tory leadership race Andrea Leadsom Minister of State for Energy at the Department of Energy and Climate Change is one of the most prominent figures in the Leave campaign, seen to have performed well in TV debates Rex Features The favourites in the Tory leadership race Liam Fox British Conservative MP and former Secretary of State for Defence, as sources said he will stand for the leadership of the Conservative Party AFP/Getty

Home Secretary Theresa May also took an apparent swipe at the former mayor this morning, writing: "Some need to be told that what the government does isn’t a game, it’s a serious business that has real consequences for people’s lives."

Mr Johnson's departure from the race leaves Ms May as the favourite to win the race. She launched her leadership campaign this morning.

The shock news comes after George Osborne, who was previously seen as the anointed successor to David Cameron, ruled himself out of the race following the EU referendum result.

Though Mr Johnson is popular amongst Conservative party activists, the party's internal electoral system allows MPs to pick which two candidates their members can vote between.

Other candidates to declare in the race so far include Work and Pensions Secretary Stephen Crabb, former defence secretary Liam Fox, and Andrea Leadsom. Health Secretary Jeremy Hunt has said is "seriously considering" a run.

The leadership election was called after Mr Cameron announced his resignation in the aftermath of the EU referendum result.