He says that Labour’s candidate has shown “bad judgement” and says that a candidate who has been “so consistently wrong” on the issue of extremism for “so long” should not the mayor of London.

Mr Goldsmith also hits out at “offensive” and “irresponsible” claims made by Labour that he and David Cameron are “racist” and “Islamophobic” for raising questions about Mr Khan’s links to Islamists.

In his interview, Mr Goldsmith also backs this newspaper’s campaign to toughen up Britain’s border controls, saying that “it is crazy” that the UK does not have “control” of who comes into the country.