Vote Leave campaign leader, Boris Johnson, raises a glass as he delivers a speech in London, Britain June 30, 2016.? [Photo/Agencies]

Boris Johnson, the former London mayor who had spearheaded the successful campaign for Britain to leave the European Union, dramatically announced he would not be running for leadership of the ruling Conservative Party, which would have automatically made him prime minister.

Johnson was widely tipped as favorite to succeed David Cameron following the prime minister's defeat in the EU referendum result and subsequent resignation on June 24.

Home Secretary Theresa May and Johnson were seen as front runners to become the next Conservative Party leader before Leave campaigner Justice Secretary Michael Gove announced Tuesday he planned to run as well.

Gove had widely been tipped to back Johnson but instead said he would run himself. Gove had been Johnson's campaign manager in the referendum.

In a ten minute speech in which he focused on his legacy as Mayor of London, Johnson ended by saying that he was not the best candidate to lead Britain as it carves a new path outside of the European Union.

"Having consulted colleagues and in view of the circumstances in Parliament I have concluded that person cannot be me," Johnson said in a press conference. "My role will be to give every possible support to the next conservative administration, to make sure that we properly fulfil the mandate of the people delivered at the referendum."

Gove joins fellow leaves campaigners Liam Fox MP and Andrea Leadsom MP in the contest, while Stephen Crabb MP and May are the two Conservative candidates for party leadership who supported Remain during the referendum.

The official list for Conservative Party leadership candidates closed after Johnson's announcement.

Opposition leader Jeremy Corbyn faces a challenge after 172 of his Labour Party legislators voted a motion of no confidence in him, and the bulk of his shadow cabinet resigned in protest at his leadership. Corbyn is refusing to stand down, saying he has aidespread grassroots support in the country.

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