Boris Johnson will not stand to be the next Conservative Party leader in the race to succeed Prime Minister David Cameron.

The former London mayor and Leave campaigner told a press conference that after consideration he had decided that the next Tory leader could not be him.

The surprise announcement comes after Leave campaign ally Michael Gove, tipped by many to back Johnson in the upcoming leadership contest, threw his own hat into the ring earlier on Thursday morning.

Johnson, who was expected to announce his own candidacy for leader at the press conference, said: "Having consulted colleagues and in view of the circumstances in parliament, I have concluded that person (to lead the party) cannot be me.

"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 that was delivered at the referendum and to champion the agenda I believe in - to stick up the forgotten people of this country."

Gove said he could not support Johnson as he does not believe the former London mayor can "provide the leadership" the country requires.

He said he would therefore run for party leader himself, adding: "In the next few days I will lay out my plan for the United Kingdom which I hope can provide unity and change."

Home secretary Theresa May also formally announced her candidacy for the role at a speech in London on Thursday morning.

She said: "My pitch is very simple. I'm Theresa May and I think I'm the best person to be Prime Minister of this country."

In addition, Stephen Crabb, Liam Fox and Andrea Leadsom have been confirmed as the official Tory leadership contenders by the chairman of the 1922 Committee, Graham Brady.