London mayor to campaign for 'Brexit

London Mayor Boris Johnson yesterday said he backed leaving the European Union, dealing a blow to Prime Minister David Cameron by giving the "out" campaign a de facto leader who is one of the most charismatic politicians in British politics.

Cameron announced a June 23 referendum on Saturday after clinching a deal from 27 other leaders to give Britain what he said was a special status.

But Boris remained silent on Cameron's deal for nearly two days before making his dramatic announcement on the steps of his north London home.

"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," Johnson told a crowd of reporters.

British voters - and Cameron's ruling Conservative Party - are split on membership. Polls suggest about a fifth of voters are undecided, though one poll published on Sunday showed the "in" campaign with a lead of 15 percentage points.

Pro-Europeans have warned that an exit could also trigger the break-up of the United Kingdom by prompting another Scottish independence vote if England pulled Scotland out of the EU.