Police to lose '10,000 officers by 2013'
At least 10,190 uniformed police officer posts are set to disappear by the end of next year in England and Wales, Labour Party research suggests.
Shadow home secretary Yvette Cooper said "cutting so fast and deep" was "irresponsible" and "crazy".
The coalition's Spending Review set police budget cuts at 20% by 2014-15.
Policing minister Nick Herbert said he did not accept the figures, adding it was the effectiveness of officers not their total numbers that counted.
The Police Federation, which represents police officers, said numbers were on track to fall back to the level of the 1970s.
Chairman Paul McKeever said: "We're going to be back below 215 officers per 100,000. We're 257 at the moment, and I'm one of the very few police officers old enough to remember what it was like back in the 1970s.
"We really were in meltdown then, it was very bad news indeed. We've improved enormously over the last 30 years, through increased funding and the resources we've had, and we're going to lose an awful lot of that."
Shadow home office minister Vernon Coaker told the BBC budget cuts were already having an impact on the front line.
"David Cameron said that if any minister came to him with proposals which hit front-line services then he would send them away," he said.
"And clearly what we're seeing in respect to the police, we're seeing cuts in police officer numbers which are already impacting on neighbourhood policing teams, already impacting on specialist units."
BBC political correspondent Laura Kuenssberg said Home Secretary Theresa May had always insisted that the cut in police budgets of 4% this financial year and 5% next year, should not have to mean a cut in the number of police officers.
But after Labour collated figures from all 42 police authorities in England and Wales - except the British Transport Police - the party claims that hope cannot be realised.
Of the 42 analysed by Labour, two-thirds had made recent announcements on police numbers whilst a third had not yet declared how the budget cuts set out in the Spending Review would affect them.
For forces included in that third, Labour used police figures from May to September last year.
The government has always insisted that front-line jobs can be protected, despite the savings they want.
Mr Herbert said forces can and must make savings in their back and middle offices.
"By sharing services, outsourcing and procuring equipment together, they can work more efficiently and prioritise the front line, so that the service to the public is maintained and improved," he said.
"Despite officer numbers reaching record levels, only 11% are visible and available to the public, not least because of Labour's red tape.
"It's not the total size of the police workforce that counts - it's how effectively officers are deployed."
Ms Cooper said their figures for the next two years were "only the beginning", with a third of forces yet to announce their cuts for next year. Most of those that had announced their cuts had only looked at the next two years, she added.
"Cutting so fast and so deep into police budgets is crazy. It is completely out of touch with communities across the country who want to keep bobbies on the beat," said Ms Cooper.
She later told Sky News: "It's just irresponsible. Police forces are put in an impossible position... they're trying to do their best and having the rug pulled under them.
"They cannot protect front-line policing if they're faced with this scale of 20% cuts. These plans are out of touch with what people across the country will be thinking about the need to tackle crime."
But Mr Herbert insisted police numbers would also fall under Labour's plans, and it was "totally dishonest" to pretend otherwise.
"I don't accept Labour Party figures," he told the BBC's The World This Weekend. "I think it is better to wait for official figures. We have never said we can guarantee police numbers and nor has the Opposition said that."
He added: "I think it would be quite wrong to imply there would be this impact on frontline policing which every chief constable is determined to prioritise [against]."
The head of the Police Superintendents' Association, Derek Barnett, said whilst they can reduce bureaucracy and streamline back office services, there would "inevitably" be an impact on front-line services.
The Association of Chief Police Officers said there were difficult choices ahead for the police service, for police partners and for government.
A spokeswoman said: "The cumulative impact of cutting police budgets year-on-year will translate into reductions of police officers and staff across the service.
"The extent of the cuts will depend on the financial circumstances of each force and the different reliance that each force has on local and central funding streams.
"Every chief officer remains committed to doing all they can to protect front line service delivery to the public."