British style of policing is "on its knees and facing extinction", according to the Police Federation.
In a dire warning, it said that police and the public are being exposed to "increased risk" as more frontline officers are forced to work alone because of stretched resources.
A survey released by the federation, which represents rank and file officers in England and Wales, suggests almost nine in 10 feared there were not enough of them to manage demand while 76% of respondents from frontline roles reported "often or always" working alone – known as single-crewing.
The results have been branded a "huge red flag" to the government by the federation.
The federation also reported that serious extent of stress and anxiety among officers, with some being described as "traumatised".
National vice-chair Che Donald said: "When officers work alone they are undoubtedly exposed to increased risk, for them and the public, not to mention the detrimental effect on their overall health and well-being."
He added: "Forces are having their hands forced as they struggle to meet the increased demands placed on them, but this false economy of single crewing merely creates the illusion of public safety.
"Quite simply this is not sustainable and officers are suffering."
The federation’s demand, capacity and welfare survey, published on Wednesday, saw more than 18,000 officers from the rank of constable to chief inspector give their views on demand and how this has affected them.
The survey found almost every officer had been exposed to at least one "traumatic experience" in their career, with 62% saying they had experienced at least one in the last 12 months.
It also found nearly eight in 10 officers had felt stress and anxiety within the last 12 months with 94% of those saying this was caused or made worse by their job.
About 44% of respondents said they viewed their job as "very or extremely stressful", a larger proportion than the 39% in a similar 2016 survey.
Mr Donald said: "The police service’s most valuable resource is its people and these results should be a huge red flag to the Government, chief constables and the public."
He said that since 2010, austerity cuts had resulted in almost 22,000 fewer officers and an "over-stretched service staffed by stressed and traumatised officers".
He added: "The once revered British model of policing is currently on its knees and facing extinction, we need to act now to save it."
But policing minister Nick Hurd said the police service was being given increased investment to recruit more officers.
He said: "The Home Secretary and I have been crystal clear that policing’s greatest asset is its people and we are determined to ensure that forces have the support and resources they need to protect the public.
"I am delighted that Parliament has approved our funding package for next year, which will increase investment up to £970 million, including money raised through council tax.
"This funding settlement recognises the demands on police forces and police and crime commissioners are already setting out plans to recruit more officers as a result.
"We take the well-being of police officers and staff very seriously, which is why we launched the Front Line Review to listen to their concerns and have invested £7.5 million in a new national police well-being service."