British counter-terror agencies have been "stretched" by a recent spate of atrocities, potentially compromising efforts to quash future threats, the Metropolitan Police Commissioner said.
Four terror attacks in the UK this year, including two in London this month, have diverted resources as officers meticulously examine the plots, Cressida Dick told the London Assembly.
The country's most senior officer told the Police and Crime Committee other criminal investigations have been paused or delayed out of "necessity".
Vehicle-based attacks have blighted the capital since March, most recently when crowds of Muslim worshippers were mowed down by an alleged attacker near Finsbury Park, north London, on Monday.
Ms Dick said: "The counter-terrorism network is certainly stretched. Before 12 weeks ago, they had a set of people and they still have a set of people across the country in essence.
"They have now had four major attacks to deal with and also disrupted a number - five - other plots.
"Those all take a great deal of backward-looking investigative resources and it takes potentially away from the proactive and forward-looking intelligence work.
"We have supplemented the national counter-terrorism network from some of our crime resources nationally and within London and we need to do that.
"We are shifting resources and people across the Met.
"This does have an impact on other, for example, investigations, we have had to pause some, we have had to slow down on some, and that is just a necessity.
Despite the wave of major incidents, which also included the police response to the Grenfell Tower fire in west London last week, the force remained "steely in its determination", Ms Dick added.
Appearing to answer questions from the committee for the first time, Ms Dick said the overtime bill to date for the London Bridge attack, which she said "remains a very large investigation", is £1.2 million.
She revealed that 4,100 exhibits were seized as part of the operation in the wake of the terrorist outrage on June 3 - which saw three attackers kill eight people with a van and knives.
Ms Dick highlighted that in between the two terrorist incidents there was also the fatal Grenfell Tower fire, which she said is a "further very significant major incident".
Ms Dick said the force is currently working with the London Fire Brigade and independent expert building examiners as part of the wider ongoing inquiry.
She told the committee Scotland Yard has 260 officers dealing with the main investigation and identification of blaze victims.
The commissioner's warning comes on the heels of an intervention by the country's leading counter-terror officer about the risk of directing resources from other policing priorities.
Assistant Commissioner Mark Rowley said in a letter to the Home Secretary that the fight against terrorism could have a "significant impact" on combating other crime in England and Wales.
He said counter-terror efforts could not operate at "full strength" as detectives were also working in greater numbers on areas such as child abuse.
The Home Office claimed "detailed engagement" is under way with police over potential funding changes, after Ms Dick told it the Met could not cope with further cuts.
Van rental could be subject to more stringent checks after hired vehicles were used in all of the recent London terror attacks, Ms Dick suggested.
"Obviously we sent a message to the hire community to say 'Please be careful. Think who it is - think if there's anything suspicious. Please let us know'," she said.
"But should that be regulated in any further way?
"There is a whole big review to be done which might require some legislation, I don't know. It might require some tweaking of legislation; for me it is in the community."