The huge counter-terrorism effort launched in the wake of recent attacks is placing an unsustainable strain on Britain's wider policing service, one of the country's most senior officers has warned.
Sara Thornton, the chair of the National Police Chiefs' Council (NPCC), says the "flat cash" funding settlement for forces announced by ministers two years ago is no longer enough.
The warning comes six months to the day since the Westminster attack, the first of five terror attacks in the UK this year.
"The money that the government spends on countering terrorism is going up to £15 billion by the end of this government, but in fact the percentage that is spent on policing is very small, about £700 million or 5%," said Ms Thornton.
"For the next two years that money is set to reduce by just over 7% and we're really quite concerned about that given the fact that what we seem to be dealing with is not a spike in terrorist activity but a complete shift."
The former Thames Valley chief constable said the raising of the terror threat level to critical following last Friday's Parsons Green tube bombing led to forces across the country deploying officers to protect the public, putting "tremendous strain on policing". It is a trend which she has become all too familiar with in recent months.
"In the response to the Manchester attack, three quarters of the resources deployed came from mainstream policing," added Ms Thornton.
"This disrupts the daily work of policing on which the public rely, it creates backlogs of incidents in our control rooms and results in a slower response to the public.
"With officer numbers at 1985 levels, crime up 10% in the last year and police work becoming ever more complex, this additional pressure is not sustainable."
Police and MI5 are running 500 live investigations involving 3,000 individuals, while another 20,000 former "subjects of interest" must be kept under review.
Authorities have foiled 19 plots since the middle of 2013, including six since Westminster.
A Home Office spokesman said:"The government will do what it takes to keep families, communities and our country safe.
"That is why we are increasing funding for counter-terrorism by £3.4 billion and the Home Secretary announced £24 million in extra support for 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."