An ambulance service has disclosed a dramatic increase in the numbers of suspected stroke and heart attack patients having to wait more than an hour for a vehicle to take them to hospital.
In the past three years, the number of such patients kept waiting more than 60 minutes by the East of England Ambulance Trust has more than quadrupled.
In an internal email seen by the BBC, staff at the East of England Ambulance Service have called on the trust board to investigate "the vast numbers of patients that have deteriorated due to the current operational policies of this trust".
It is understood a collective grievance has been raised by crews in Peterborough over a policy of getting more of them to work alone using rapid response vehicles in order to meet response time targets.
They claimed not enough priority is being given to actually transporting patients to hospital in back-up ambulances.
They also claimed many of these ambulances are being diverted elsewhere, also to meet targets.
The email, which was sent to ambulance stations across Cambridgeshire, Suffolk and Norfolk, described how staff had also gained access to the trust's own internal databases.
It said some staff had presented management with documentary evidence of "hundreds of patients, many being time critical stroke and PPCI patients, that have had to wait in excess of an hour for transport".
PPCI is a surgical procedure for treating a heart attack.
The ambulance trust's own figures, obtained by the BBC, show that in 2010-11, there were 351 occasions where a vehicle called to a patient with a suspected stroke or heart problem took more than an hour to arrive on scene.
This is up from 72 in 2007-08.
The trust said the number of such calls it received almost doubled over the same period, to more than 27,000 a year.
Internal inquiry call
The email outlining the grievance follows an incident in Peterborough on 26 June in which a 56-year-old woman who suffered a stroke at a restaurant had to wait more than an hour for an ambulance to take her to a hospital just two miles away.
Theresa Bradshaw's family have confirmed that the vehicle which eventually turned up had travelled from Huntingdon, 20 miles away.
Mrs Bradshaw did not survive, though it is understood that an earlier ambulance may not have saved her.
The internal email also said staff planned to raise the issue with the Care Quality Commission and MPs, if their call for an internal inquiry was unheeded.
According to Department of Health figures for April, the East of England Ambulance Service was the worst performing in mainland England for getting stroke patients to a specialist unit within an hour.
The ambulance service's figures show that 47% of stroke patients got to a specialist unit within an hour - half as well as the best performing trust in England, though this had climbed to 57% in May.
The East of England Ambulance Service admitted it became aware of problems with back-up vehicles getting to patients four months ago.
In a statement, the trust said: "Demand is now at a record high after a 15% rise in calls in the last three years.
"It has been therefore necessary to implement more appropriate and effective ways of delivering our service to patients during challenging times.
'Put at risk'
"We take any delays in back-up very seriously and each case is now automatically flagged and investigated. As a result of thorough research into the issue we have drafted robust proposals to address it."
The trust said it had now recruited a manager with a specific responsibility to cut back-up times.
Norman Lamb, the Liberal Democrat MP for North Norfolk, said that he had also been approached by trust staff voicing the same complaints over delays to back-up vehicles.
He said he was writing to the Care Quality Commission, calling on it to investigate the trust's practices.
Ian Maidlow, regional officer for the Unite union, which is representing the Peterborough staff, said: "We're extremely concerned. We believe that patient care is being put at risk and that the professional integrity of our members is being undermined."