London Mayor Sadiq Khan has pleaded to Boris Johnson to recruit police officers "much, much quicker" because the capital’s Metropolitan Police is “under-resourced and overstretched”.

Mr Khan warned the city needs more officers to deal with knife crime than the 20,000 pledged by Mr Johnson over three years, having lost 21,000 under consecutive Conservative governments.

He added that the police force’s “preventative side”, such as youth clubs, have been slashed under austerity, fuelling a rise in knife crime.

He said police were using their stop and search powers in the way Mr Johnson favours, but stressed that there are simply too few officers left, in an interview with broadcaster Iain Dale at the Edinburgh Fringe.

Asked about whether the force had "London under control”, Mr Khan said it needed more support from the government.

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“We’ve got fewer police officers now than any time since 2003, while the population has risen by two million,” Mr Khan said. "Are the police worried about the lack of numbers? The answer is yes. Our police work so hard. They are under-resourced and overstretched.”

He said he was using money from London’s City Hall, from council tax and business rates, to recruit more officers.

"In the eight years before I became mayor, Boris Johnson never raised council tax to pay for police,” he added. “In my first three years, I've raised council tax the maximum I'm allowed to do by law to divert it to the police.

"Our police is funded by roughly 80 per cent by central government and 20 per cent by other sources. It's now gone down to 70 per cent from central because I've raised other sources, but I can't fill the massive hole left by £1bn of cuts."

Mr Khan said he had not yet spoken to the prime minister since Mr Johnson took office, although he had written to him after the former London mayor was elected by Conservative Party members.

There was no sense of admiration by Mr Khan for his predecessor, as he branded Mr Johnson as a “liar” who had filled his cabinet with ministers who have “seriously obnoxious views”.

"I'm 48-years-old and I can't remember a more right-wing government in my lifetime,” he said, citing those with opposition to abortion and LGBT+ rights in Mr Johnson's cabinet.

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Asked about his ongoing feud with Donald Trump, who recently claimed London would "never have safe streets" with him as mayor, Mr Khan joked: "I have no idea what Donald Trump has against the Muslim Mayor of London."

He added: "We've all got to be vigilant to the fact that you've got the president of the USA who has views that are paraded by terrorists in Christchurch, by terrorists in El Paso, by terrorists in this country and by terrorists all over the world. That should worry us."