Guy Hands, the multimillionaire founder of private equity firm Terra Firma Capital Partners, said Britain should stay in the European Union, voicing concern that London Mayor Boris Johnson's support for the campaign to leave the bloc could sway the outcome of an upcoming referendum.

UK Prime Minister David Cameron has called for Britons to vote to stay in the EU in the referendum on June 23. The decision by Johnson - a fellow Conservative seen as a contender to lead the party one day - to campaign to leave, was a blow to the prime minister.