London Mayoral Candidate Sadiq Khan has refused to rule out putting up his share of council tax.

hopeful said he would keep the tax “as low as I can” but could not match Zac Goldsmith’s pledge to freeze.

In a lively Evening Standard debate - which covered issues ranging from extremism, to the EU referendum and the housing crisis - he warned that he had to protect City Hall income in case George Osborne launched a raid on policing.

Scotland Yard has already been forced to cut £600 million from its £3.5 billion budget and a cross-party coalition of MPs fought off a further £800 million cuts last autumn.

Mr Khan, the frontrunner, came under pressure to confirm his plans on council tax after asking recently how a “serious candidate” could freeze the levy.

After refusing to answer three times, he told the audience: I will keep it as low as I can but I can’t promise to freeze it over the next four years. Here’s why you can’t make a promise to freeze council tax without risking our security. What happens if the Chancellor comes back next year, or the year after?”

Mr Goldsmith said he would be able to freeze the precept - about £276 a year for a Band D property - because he had secured a deal with ministers to protect police numbers at 32,000.

“I believe we can go further, but I’ve not promised things in my manifesto that I’m not absolutely certain I can deliver,” he said.

The Mayor’s precept is worth £767 million a year, with £567 million going on the Met, £138 million on the London Fire Brigade and £69 million for services including transport and City Hall itself.

The Tories claimed Mr Khan’s remarks meant it would double in order to pay for his spending commitments - which they estimate at around £3 billion - but experts questioned their analysis.

Local authorities are currently barred from putting up council tax by more than two per cent without holding a referendum of local people.

Mr Khan has promised to freeze fares which are the Mayor’s single biggest independent income stream - around £4.6 billion last year. 

His Tory rival has only said he would try to “bear down” on fares - claiming Labour’s “irresponsible” plans would result in a £1.9 billion black hole at TfL.

You can do it, but you can’t do it and grow the transport network, for commuters it would be hell,” he said.

The extremism row circling over the mayoral campaign threw a shadow over the debate as both men insisted they had done nothing wrong.

Mr Goldsmith, whose campaign was accused by Labour of being “divisive” and “racist” for highlighting how often Mr Khan had shared platforms with extremists, said: “I’ve never led a political campaign that has been anything other than entirely positive.

He added: There are issues that I have raised and that Londoners have raised, that question not Sadiq Khan’s views, but his judgement.

Mr Khan has not denied coming into contact with extremists but has always pointed to his past as a human rights lawyer and chair of human rights group Liberty by way of explanation. He insisted he had spent his whole life fighting extremism.

“The clear choice at this election is between a united London and a divided London, between a One London approach with a mayor for all Londoners and a Donald Trump approach with a mayor for some Londoners. My message is clear - choose unity over division, choose hope over fear,” he said.

He claimed that senior members of the Tory party had told him they were “disgusted” with Mr Goldsmith’s campaign - but refused to give names.