By 17 March, there had been almost 500 confirmed cases in London and 23 deaths, whilst the Mayor of London Sadiq Khan announced the London Underground would begin running a reduced service due to the virus.[3] A day earlier the UK prime minister Boris Johnson had stated at a press conference that London's outbreak was a few weeks ahead of the rest of the UK.[4] The city had seen the most cases of any UK region, with case numbers rising much faster in London than elsewhere in the UK.[5] As of 18 March, Southwark and Westminster were the worst affected boroughs.[6]