London mayor sides with 'No' vote in blow for PM

Politician seen as a potential successor to Cameron says he wants to leave EU

London's mayor Boris Johnson threw his weight behind the campaign for the United Kingdom to leave the European Union on Sunday, in a blow for his old friend and rival Prime Minister David Cameron who had appealed for his backing.

"After a great deal of heartache. ... I will be advocating vote 'Leave'," Johnson said, making his long-awaited announcement to a large crowd gathered outside his home in north London.