London Mayor Boris Johnson gestures as he leaves after giving a speech on the European Union, in London August 6, 2014. Johnson, widely regarded as a potential challenger to Prime Minister David ... more 
London Mayor Boris Johnson gestures as he leaves after giving a speech on the European Union, in London August 6, 2014. Johnson, widely regarded as a potential challenger to Prime Minister David Cameron, said on Wednesday he would try to run for parliament in next year's national election. REUTERS/Luke MacGregor (BRITAIN - Tags: POLITICS TPX IMAGES OF THE DAY) less 
1 / 26
Reuters | Photo By LUKE MACGREGOR / REUTERS
Wed, Aug 6, 2014 11:55 PM EDT