Forces are already said to be warning that they will have “no option” but to shift uniformed officers into support posts if a new round of austerity means civilian staff numbers are scaled back.
The Association of Police and Crime Commissioners (APCC) has submitted an analysis of the possible impact on the police service of possible cuts over the next five years.
The Home Office, which is responsible for handing out money which makes up the majority of police budgets, has been told to prepare proposals that would achieve savings of 25% and 40% by 2019/20.
The department said no decisions have been taken on police funding beyond the current financial year.
The APCC said its current modelling of possible changes suggests that police officer numbers could fall below 100,000 by 2019/20. Figures show that in March there were 126,818 officers working in the 43 forces in England and Wales.
The analysis said: “Even if uniformed staff reductions do not exceed the levels of natural turnover, the forecasts imply that police officer numbers will fall below 100,000 by 2019/20.”
There are already signs of “unavoidable actions which may compromise some of the beneficial changes from the past”, according to the report.
It said: “The best example is use of uniformed staff to undertake desk-based roles. Civilianisation has been one of the success stories of the last 15 years.
“There are no restrictions on the use of both voluntary and compulsory severance for non uniformed staff, but the options available on uniformed staff are more restricted.
“If overall establishments need to be further reduced - and there is no realistic alternative - some forces are already warning that they will have no option but to transfer police officers back into support roles.”
More savings needs
Controversy over the possible impact of new cuts erupted earlier this year when a senior officer suggested burglary victims may not always be visited at home.
The Home Office said future funding levels will be subject to the outcome of a spending review which will report in November.
Policing minister Mike Penning said: “Police reform is working. Over the last five years, frontline services have been protected, public confidence in the police has gone up and crime has fallen by more than a quarter, according to the independent Crime Survey for England and Wales.
“There is no question that the police still have the resources to do their important work. What matters is how officers and staff are deployed, not how many of them there are in total.
“The changes the Government have made since 2010 have made it easier for the police to do their job by cutting red tape, scrapping unnecessary targets, and giving officers the discretion to use their professional judgment.
“Decisions on the operational deployment of resources are matters for Chief Constables in association with Police and Crime Commissioners.”
Alex Marshall, chief constable of the College of Policing, said it has looked at the demand on police services.
He said: “Evidence shows that while the number of recorded crimes may have fallen, the level of demand on police resources has not reduced in the same way.
“The College foresees a future where there will be fewer people working in policing with less supervision and we need to ensure officers and staff have access to the skills, knowledge and information they need to succeed in protecting the public and reducing crime.”