The Government must wake up to the reality of a "Christmas for criminals" as up to 40,000 police officers could be axed if 25% funding cuts go ahead, the Police Federation has said.
The body, which represents officers in England and Wales, said forces would be left "devastated" and specialist departments - including those involved with child protection and domestic violence - would "disappear" as resources were diverted to calls needing emergency responses.
Paul McKeever, the federation's chairman, warned that the cuts, coupled with Justice Secretary Kenneth Clarke's desire to see more offenders dealt with in the community rather than with short-term prison sentences, would be a "volatile mix".
"Our officers are telling us the most vulnerable in society will be hit the hardest", he said.
"Those who can protect themselves, will go and protect themselves. Those who can't protect themselves will be at greater risk of experiencing anti-social behaviour, violent crime and crime generally. We will be delivering a lot less, in fact we'll be stopping delivering in some areas altogether."
There were already plans for the domestic violence unit of the Northamptonshire force to be absorbed into the major crime unit, effectively depriving the force of those specialist services, he said.
The warning was made as Hampshire Constabulary announced it would axe 1,400 posts, including hundreds of police officers, as it cuts about a fifth of its workforce in a bid to make £70 million worth of savings over the next four years.
One national estimate found 60,000 frontline and civilian jobs in the police service would be at risk if the cuts went ahead at 25%.
Mr McKeever said he was "surprised" that the police were not in the lower bracket of cuts, but instead had been told to prepare for reductions of 25% or more.
He blamed "bad advice" from the Home Office and think-tanks which suggested that big enough savings could be made through efficiencies to justify a 25% cut.