London's mayor Boris Johnson to call for reform of EU - Sunday Telegraph

London Mayor Boris Johnson speaks at a rally in west London May 21, 2014. REUTERS/Suzanne Plunkett

LONDON (Reuters) - The mayor of London, Boris Johnson, will call for reform of the European Union in a speech on Wednesday and back a report by his economic adviser that says leaving the EU is a "viable option" for Britain if it cannot change, a newspaper reported.

British Prime Minister David Cameron has promised to renegotiate Britain's relationship with the EU ahead of a referendum on membership by 2017 if his Conservatives win a national election next year.