Three police forces have been given approval to order their officers to retire as a way to cut costs, the BBC has learned.
North Wales, Strathclyde and Surrey police authorities have all now backed the plan in principle.
Fully sworn officers cannot be made redundant, but regulations state that they can be "required to retire" after 30 or more years' service.
Police federations said they were concerned at the speed of the move.
Fully sworn officers are Crown servants, not employees, so cannot be made redundant. Other than freezing recruitment, the only option to cut staff numbers is to implement regulation A19, which is contained in the Police Pensions Regulations 1987.
This little-used measure states that all police below chief officer rank, with at least 30 years of service, can be "required to retire" if their retention would "not be in the general interests of efficiency".
Police Federation vice-chairman Simon Reed described it as a "blunt instrument", which could lead to officers experienced in such areas as child protection and serious criminals, as well as those on the street, being forced to retire.
"We're ill-equipped to lose people of that magnitude," he said.
The BBC understands that A19 could be used against about 35 Surrey Police officers over the next four years.
Chief Constable Mark Rowley said it was a "difficult decision for the force", but "hard choices" were unavoidable.
"The public would expect me to do everything I can do to organise the force in a way that there's as many officers on the front line, visible and accessible, doing what they want them to do," he said.
"This decision's about protecting that, because we're only applying it to inspectors through to chief superintendents - senior officers."
The local police federation in North Wales predicted that 53 officers could be retired by April if A19 were introduced and some 250 could be affected over the next four years.
North Wales Police said "no decision has been made on timescales", but Alun Lewis, chair of the police authority, said the chief constable had been given the authority at the end of September to formally consult with staff on agreeing a "fair and transparent selection criteria".
Federation secretary for North Wales Richard Eccles said: "What is worrying is the speed of this probably happening over the next couple of months - we are probably going to lose something like 1,500 years of policing experience between now and the end of March, which is quite a serious concern."
'This will spread'
Plaid Cymru's parliamentary leader Elfyn Llwyd said it was "not acceptable".
"You get rid of all that experience, it's going to be more difficult for young people to get fully trained up," he added.
Strathclyde Police said regulation A19 could affect 110 officers in his force, of whom 55 were understood to be on the verge of retirement anyway.
However, the police authority stressed that approval was in principle only, and implementation could be cancelled if financial and legal problems arose.
The police authority is also awaiting news of how much money the force will receive following the Scottish Budget statement on 18 November.
It is understood that Lothian and Borders, Central Scotland Police, Dumfries and Galloway, and Northern Constabulary have also been discussing the implementation of regulation A19.
Les Gray, chairman of the Scottish Police Federation, said: "We'll take legal advice, speak to our members and take it from there.
"This will spread throughout the whole of the UK. Police officer numbers will fall dramatically because there is no recruiting ongoing."
A Scottish government spokesman said the Spending Review had delivered "a bigger-than-expected cut of £1.3bn to Scotland's budget", but insisted Holyrood was committed to protecting frontline policing.
"At present, around a quarter of the total police budget is spent on the headquarters functions of the eight police forces, making it appropriate for us to examine the future structure of Scottish policing in partnership with the police and all relevant bodies."
Michelle Mitchell, director of Age UK, said the move "flies right in the face of equality legislation and runs contrary to the government's plan to abolish forced retirement" at 65.
"The huge pressure to slash budgets is no justification for bypassing basic equality principles which should withstand even the toughest economic and political environment," she said.
A Home Office spokeswoman said the issue of whether or not to implement regulation A19 was a matter for individual forces.
But shadow home secretary Ed Balls said it would "mean losing some of our most experienced people from the police service".
Ministers have said that central government funding for police in England and Wales will fall by 20% over the course of the Spending Review.
However, the total cut may turn out to be only 14%. That is because police authorities are under pressure to raise the precept, the amount of a force's budget that comes from council tax.
Officials have not published figures for the number of police and civilian staff job losses - but insist that claims of between 40,000 and 60,000 are wrong.