David Cameron has been accused of misleading the House of Commons about the number of police on the streets of Britain in the wake of the Paris terror attacks.
The accusation comes amid a row between the police and the government over George Osborne's expected announcement of further cuts to police budgets in next week's spending review.
A leaked letter sent by senior police chiefs to the home secretary Theresa May warned cuts beyond 10% would "severely impact" on the force's ability to cope with a terrorist attack.
Quizzed by Jeremy Corbyn during prime minister's questions on Wednesday, Cameron said neighbourhood policing numbers had risen on his watch.
But in a letter sent to Cameron and seen by The Huffington Post UK, Labour's mayoral candidate Sadiq Khan said this was not true.
"Londoners owe a debt of gratitude to the Met Police who do such a sterling job keeping the city safe. But since you became Prime Minister, the ability of the police to do their job has been seriously challenged because of cuts to the number of officers in London," he wrote.
"Since May 2010, there has been a reduction of 11 per cent in the number of police officers, and a 74 per cent cut in the number of community support officers.
"That is why I was surprised to hear you say at Prime Minister’s Questions today that 'neighbourhood policing numbers have gone up by 3,800 in the capital city we have seen a 500 percent increase in neighbourhood policing.'
"However, I have searched the data and I’m afraid that I simply do not recognise your figures. Londoners deserve honesty about the impact of your Government’s cuts on the number of police on the city’s streets, and it is therefore crucial that you correct the official record as swiftly as possible.
Khan added: "Your misleading use of statistics comes at a challenging time for policing in the capital. The current Met Commissioner, Bernard Hogan-Howe, has warned that a further 5,000 police officers could be lost from London as a result of next week’s spending review cuts. Given recent horrific events in Paris, many Londoners are very worried about how we keep the city safe should a similar attack take place in the capital."
In response the Home Office said the figures quoted by the prime minister came from the latest statistics supplied by the Metropolitan Police.
Labour's shadow home secretary Andy Burnham last night told BBC Question time that cuts above 10% would be "dangerous and put public safety at risk"
And Steve White, chairman of the Police Federation of England and Wales, told the Today program this morning: “We are saying we can barely cope now. If there are going to be further cuts to the police cuts, quite frankly, god help us. We are not going to be able to respond to something on the scale of Paris."
But former Conservative police minister Damian Green dismissed the letter from the senior police chiefs as "froth". He told the same programme: "At a time where money is not flowing freely, if you reorganise the police effectively and they have reorganised themselves effectively you can release resources so you actually get more police out on the streets where they can do most good.
"You can protect the counter-terrorism budget which is clearly hugely important in the current climate and that's something which I would hope to see continuing."