London Mayor Boris Johnson has become involved in the row about the government's chief whip Andrew Mitchell and police officers guarding Downing Street.
Mr Johnson has backed the police officers who threatened to arrest Mr Mitchell.
The Mayor was speaking after a leak of the official police log of the encounter between the politician and the police.
Mr Mitchell has apologised for his outburst but denies using the words being quoted.
This report from our Political Correspondent Simon Harris.
More top news
Corbyn was unveiling a poster less than a mile away as Khan gave his final campaign speech to party supporters in London.
Hay fever is an allergic reaction to airbourne pollen. There are 2 million sufferers in London (that's one in 5 people).
The man suffered head injuries after falling from Westminster Bridge and landing on concrete steps.