Helicopters carried personnel and did reconnaissance for up to 13 hours during the Westminster Bridge and Borough Market attacks.
But they can only fly for two to three hours at a time, so each major incident takes up five or six of the UK fleet of 19. That meant other calls for police air support had to go unanswered, officers warned.
The concerns are revealed in minutes for a meeting of the National Police Air Service (NPAS). It cited the attacks in London and Manchester, the Grenfell fire, and the “Justice for Edson” protest march in Stratford in June.
Details of how many requests for air support had to be turned down during the London attacks were redacted from the minutes, but sources said services were restricted both during the incidents and for some time afterwards.
NPAS raised the threshold for “Threat, Harm and Risk” used to gauge whether or not to dispatch helicopters.
The annual spend on helicopters has been slashed from £53.5 million in 2012 to £38.5 million now with eight out of 23 police airfields shut and the service centralised.
Phil Matthews, a former helicopter air observer seconded to the Police Federation, said: “It is frustrating; there’s a lack of resources, and when you get a major incident, service to other incidents inevitably suffers.”
The aircraft can save lives during car chases and rescues but often only make a big difference if they arrive quickly, he said. Shortages were worsened because of an ageing fleet. Six helicopters were retired last year but four new reconnaissance planes were yet to arrive.
The minutes say NPAS wrote to Home Secretary Amber Rudd in March and June “highlighting concerns around future fleet strategy and financing” but received no response.
NPAS chief Mark Burns-Williamson called that “unacceptable” at the meeting in June. The Home Office has since asked for fully costed proposals to renew the fleet. Chief Constable Dee Collings of West Yorkshire Police, which runs NPAS, said: “We’ve had some challenges but nothing I would not expect as the first ‘pathfinder’ national policing capability.”