Britain's most senior counter-terror officer has delivered a stark warning to ministers over the impact on forces as they attempt to contain the unprecedented threat.
Assistant Commissioner Mark Rowley suggested other policing priorities in England and Wales could be at "significant" risk if resources are diverted to fight terrorism.
In a letter to the Home Secretary Amber Rudd, he also warned that the counter-terror policing network was not able to operate at "full strength".
He said demand for increasing numbers of detectives in areas such as child abuse has prevented this, according to the BBC.
The senior officer suggested that prioritising counter-terrorism work would involve "difficult choices" about resources.
He said: "It will inevitably push risk to other areas of policing, potentially with significant impact."
The letter, sent a week before the Finsbury Park attack, included a plea to avoid "uncertainty over funding" so that chief constables did not "shy away" from important operational changes.
The resources of police and security services have come under close scrutiny after four terrorist incidents this year.
Counter-terror units are working at a record pace to dismantle plots, with 18 stopped since 2013 - including five since the Westminster attack in March.
MI5 and police are running 500 investigations involving 3,000 individuals at any one time, with a further 20,000 former "subjects of interest" kept under review.
In addition to supporting intelligence agencies' work to counter the threat from Islamist terrorism, police are responsible for leading efforts to track far-right extremists.
Hundreds of officers have been working on four major inquiries launched following the attacks in Westminster, London Bridge, Manchester and Finsbury Park.
The BBC reported that a three-month plan to intensify counter-terror activity was put in place after the first three atrocities.
A spokesman for the National Police Chiefs' Council said: "We are facing an unprecedented terror threat and it is no surprise that our resources are currently tested against what is now four terrorist attacks and five thwarted plots in very short succession.
"Police chiefs, within the counter-terrorism network and beyond, have been clear that, while everything is being done to keep people safe, we are facing an extremely challenging period.
"As you would expect, we are having discussions with the Government about police funding in the long term.
"We are also looking at our resilience over the coming months and have agreed plans across policing to confront the heightened threat and protect our communities."
The Home Office said the Government has protected overall police funding in real terms, and is providing £144 million to increase armed policing capability and funding for an additional 1,900 officers at security and intelligence agencies.
A spokesman said: "Keeping families, communities and our country safe is this Government's priority.
"After the recent horrific attacks, the Government and police are in complete agreement that we must review our counter-terrorism strategy to tackle the changing threat.
"Alongside this we remain committed to increasing cross-government spending on counter-terrorism by 30%, from £11.7 billion to £15.1 billion."
First Secretary of State Damian Green, who is effectively deputy PM, told BBC Radio Four's Today programme: "There are no police cuts. We have protected police budgets in this parliament. We have increased, hugely, the counter-terrorism budget."