The UK’s counter-terrorism effort is putting an “unsustainable strain” on policing, the head of the National Police Chiefs’ Council has said.
Chief Constable Sara Thornton said resources were being diverted from mainstream policing in England and Wales, leading to backlogs in control rooms and slower response times.
She added “this puts extra strain on an already-stretched service”.
The Home Office said it was working with police on the demands they faced.
So far in 2017 there have been five terror attacks in the UK, killing 36 people.
Earlier this year, Metropolitan Police Assistant Commissioner Mark Rowley wrote to the home secretary warning that the counter-terrorism policing network was not able to operate at “full strength”.
He added that other areas of policing would be at “significant” risk if resources had to be diverted.
In a blog post, Ms Thornton wrote: “Every time there’s a terror attack, we mobilise specialist officers and staff to respond, but the majority of the officers and staff responding come from mainstream policing.
“This puts extra strain on an already-stretched service.
“In the response to the Manchester attack, three-quarters of the resources deployed came from mainstream policing.”
She said having officer numbers at 1985 levels and crime figures up 10% in the last year created additional pressures.
The current funding for forces across England and Wales is “no longer enough” and the counter-terrorism policing budget will be cut by 7% in the next three years, Ms Thornton added.
She says a response will “never be as good as preventing” attacks in the first place.
“Fewer officers and Police Community Support Officers will cut off the intelligence that is so crucial to preventing attacks.
“Withdrawal from communities risks undermining their trust in us, at a time when we need people to have the confidence to share information with us.”
Protecting the public from terrorism may require “difficult and unpalatable” decisions, she added.
BBC home affairs correspondent Danny Shaw said this was Sara Thornton’s “most significant intervention” in the debate about police funding since the terror attacks in London and Manchester.
The Home Office says the government will do what is needed to keep the public safe.
A spokesman said: “We are increasing funding for counter-terrorism by £3.4bn and the home secretary announced £24m in extra support for CT [counter-terrorism] policing in addition to the £707m already committed for this year.
“We have also protected overall police funding in real terms since 2015 and we are sensitive to the pressures on police forces across the country.
“We are engaging with them on the demands they are currently facing.”