By John Stevens Sadiq Khan is in a nerve-racking battle to cling on as Mayor of London. The Labour politician, who has run the capital since 2016, faces a challenge from Tory Susan Hall. If he is ousted it would be a major upset. Ms Hall has faced criticism over her divisive views , including support of Donald Trump. Mr Khan has won praise for his introduction of free school meals for all primary school pupils in London. But he has faced controversy for his expansion of Ulez. The Ultra Low Emission Zone, which sees drivers of the most polluting vehicles made to pay a daily charge, was extended…