A police watchdog has raised "growing concerns" that local bobbies are being taken off the beat, as it warned some forces may struggle to cope with major crimes such as rioting or multiple murders in the next few years.
Her Majesty's Inspectorate of Constabulary (HMIC) found that neighbourhood teams are being stretched with extra work that keeps them in the office, and revealed a third of people had seen fewer police officers on patrol in the past year.
The watchdog also warned that the future of some smaller forces could be at risk in the next three to five years if recent methods used to slash budgets do not change.
Those with low police officer numbers and a low cost of policing per head were highlighted as being the most vulnerable, with Lincolnshire and Suffolk among forces deemed to be at risk.
As the watchdog's latest assessment of how the 43 forces in England and Wales are dealing with 20% budget cuts was published, inspector Zoe Billingham said: "Continuing to apply the cost reductions in the same way in the next four years as they've been applied in these four years is not an option, and we're very clear that the viability of some forces could be placed in jeopardy in three to five years' time.
"By that we mean they would have to cut too hard and too deep into neighbourhood policing and they may not be able to guarantee or maintain the service that we're currently seeing to the public."
The HMIC report also warned that smaller forces with a large area to cover or high demand could find themselves unable to respond to "unexpected events".
It said: "Limited options to make savings will inevitably drive some forces to make deeper cuts into neighbourhood policing, and they may struggle to respond to unexpected events, for example public order problems such as rioting or demonstrations or major crime such as multiple murders or kidnaps."
Ms Billingham said that although staffing in neighbourhood teams is rising by an average of 8%, this masks a trend where officers are facing red tape.
"The neighbourhood officers are being asked to do more in terms of crime investigation which takes them off the street away from the communities and spending more time in stations doing paperwork," she said.
"We see this as we go round, frontline police officers are telling us that they have less time to actually be out there doing that community reassurance, preventive policing."
The watchdog has warned that collaboration between forces to save money is inconsistent and too slow, and that IT is lagging behind.
Chief inspector of the constabulary Tom Winsor said: "Collaboration between forces, and between forces and public sector organisations, remains patchy, fragmented and overly complex and too slow.
"This report finds again that the IT supporting police officers to enable them to be more productive and efficient is poor and outdated."
The watchdog highlighted Bedfordshire, Nottinghamshire and Gwent as urgently needing to improve the way they cope with budget cuts.
Ms Billingham said: "The recurring theme in all of those forces is that they did not and do not at this moment in time have an affordable plan that we think will enable them to maintain a service to the public. That's particularly important in this last year of the spending review period because that austerity is not going to go away, so it's vital that those forces do improve quickly over this financial year and get themselves match fit."
Overall, between March 2010 and March 2015, the number of police officers has dropped by 16,300, or 11%; the number of staff is down 14,500 or 17%; and the number of police community support officers (PCSOs) is down 3,600 or 22%. More PCSOs are being lost than was originally planned - an extra 700 are going.
By March 2015 there will be 8,500 fewer officers on the front line, a drop of 7%, although forces have said the proportion on the front line will be greater, rising from 89% to 92%.
The figures come after it was revealed last week that around half of crimes are not being solved.
Data from 28 police forces in England and Wales released by the Home Office showed that in April and May this year 52% of crimes were classed as ''investigation complete, no suspect identified'', meaning that the case is closed unless new evidence comes to light.
This happened in 73% of criminal damage and arson cases, 72% of theft cases and 56% of robbery cases.
Chairman of the Police Federation Steve White said: "The report provides clear evidence that cuts are damaging the police service and officers' capacity to keep the public safe.
"The Police Federation of England and Wales has been raising issues about cuts to policing for the past four years now and we are pleased that the independent HMIC has acknowledged these issues.
"It is unacceptable that 18 smaller forces are at risk of not being able to provide the same service to the public if these cuts continue.
"It is essential that action is taken on the points the report raised, in particular addressing the potential erosion of neighbourhood policing and crime prevention due to reductions to the front line."
:: A YouGov poll for HMIC questioned 19,538 adults online in March this year and found that 36% said they saw police officers on patrol less often in their neighbourhood than 12 months previously. This was compared with 32% the previous year.