Mayor of London

LONDON, ENGLAND - MAY 16:  Sadiq Khan, the new Mayor of London waves to a member of the public as he campaigns outside Tooting Broadway Underground station with Labour Party candidate for the local by-election Rosena Allin-Khan on May 16, 2016 in London, England. Rosena Allin-Khan is a junior accident and emergency doctor and mother of two who grew up in the constituency where Sadiq Khan's election to London Mayor has prompted a by-election.  (Photo by Mary Turner/Getty Images)

Mary Turner/Getty

Sadiq Khan, the new Mayor of London waves to a member of the public as he campaigns outside Tooting Broadway Underground station with Labour Party candidate for the local by-election Rosena Allin-Khan in London

British Prime Minister Prime Minister Da...British Prime Minister Prime Minister David Cameron (L) and Mayor of London Boris Johnson wait for a train at Newark station in central England on May 21, 2014, following a visit to the town were they campaigned ahead of the Newark by-election which is due to be held on June 5. Voters also go to the polls in Britain Thursday May 22, 2014, for local council elections in England and Northern Ireland and also for European elections in England, Wales, Scotland and Northern Ireland. AFP PHOTO / STEFAN ROUUSEAU/POOLSTEFAN ROUSSEAU/AFP/Getty Images

Stefan Rousseau/Getty

British prime minister David Cameron and London mayor Boris Johnson wait for a train at Newark station in central England following a visit to the town were they campaigned ahead of the Newark by-election which is to be held on June 5

Mayor of London Boris Johnson and Chancellor of the Exchequer George Osborne meet students at Peking University in Beijing where they addressed and held a Q&A with staff and students.

Stefan Rousseau/PA

Boris Johnson, mayor of London, and George Osborne, chancellor of the UK exchequer, hold a Q&A at Peking University in Beijing

An Alternative View Of The Conservative Party Annual Conference...MANCHESTER, ENGLAND - OCTOBER 01:  (EDITOR'S NOTE: Image was processed using digital filters. Colour version not available) Boris Johnson, the Mayor of London, delivers his speech in the Main Hall of Manchester Central on the third day of the Conservative Party Conference on October 1, 2013 in Manchester, England. David Cameron has unveiled a Government pilot scheme for GP surgeries to open from 8am until 8pm seven days, backed by 50 million GBP of funding.

Christopher Furlong/Getty

Boris Johnson, Mayor of London, delivers a speech on Wednesday on the third day of the Conservative Party’s annual conference in Manchester, UK.