Boris Johnson will join the Brexit campaign
The Tory MP kept Prime Minister David Cameron guessing until 5pm on Sunday
Boris Johnson has declared that he is to join the campaign for Britain to leave the European Union.
The London mayor put an end to months of speculation, saying that David Cameron's re-negotiation had failed to deliver fundamental change in Britain's relationship with Brussels.
"I don't think that anybody can claim that this is fundamental reform of the EU or of Britain's relationship with the EU," he said.
His announcement - made outside his London home - is a huge boost for the "out" campaign potentially giving them a popular figurehead able to connect with voters in a way few other Westminster politicians can manage.
At the same time, it comes as a bitter blow for David Cameron who had long believed that his old rival from their days at Eton and Oxford would ultimately fall in behind his EU re-negotiation package.
Amid chaotic scenes, Mr Johnson insisted that he had agonised over the decision before finally declaring his hand.
"The last thing I wanted was to go against David Cameron or the Government but after a great deal of heartache I don't think there is anything else I can do," he said.
"I will be advocating vote leave ... because I want a better deal for the people of this country to save them money and to take back control."
Earlier, Mr Cameron had issued a last ditch appeal for the London mayor not to align himself with "outers" like Ukip leader Nigel Farage and Respect's George Galloway.
"I think the prospect of linking arms with Nigel Farage and George Galloway and taking a leap into the dark is the wrong step for our country," he said.
"If Boris and if others really care about being able to get things done in our world, then the EU is one of the ways in which we get them done."
Mr Johnson said that he had decided to act because the European "political project" was "in danger of getting out of proper democratic control".
"Sovereignty is people's ability - the ability of the public - to control lives and to make sure that the people they elect are able to pass the laws that matter to them. The trouble is, with Europe that is being very greatly eroded," he said.
"You have got a supreme judicial body in the European Court of Justice that projects down on this 500 million people territory a single unified judicial order from which there is absolutely no recourse.
"In my view, that has been getting out of control. There is too much judicial activism, there is too much legislation coming from the EU."