A private ambulance service whose staff failed to spot a grandmother's decline as she "died whilst sat between them" has been suspended.
Peggy Copeman, 81, died while being returned to Norfolk from Somerset in 2019 by Premier Rescue Ambulance Service (PRAS).
The Care Quality Commission (CQC) suspended it following an inspection prompted, in part, by Mrs Copeman's death, concluding "people using the service may be exposed to the risk of harm".
PRAS has been contacted for comment.
Mrs Copeman, of New Buckenham, Norfolk, was transported to the specialist Cygnet Hospital in Taunton, Somerset for mental health treatment on 12 December 2019.
She was returning home four days later when she died on the hard shoulder of the M11.
Prior to the full inquest later this month, Norfolk's senior coroner Jacqueline Lake issued a prevention of future deaths report to PRAS.
Ms Lake said that during the journey on the M11, Mrs Copeman had "altered breathing" and was later unresponsive.
She said an expert witness was "of the firm view that the staff transporting Mrs Copeman did not recognise she was in respiratory distress and/or cardiac arrest and that she had effectively died whilst sat between them".
The report said only one staff member escorting her had CPR training, and none recognised she was in difficulty.
Mrs Copeman's death, alongside other factors, prompted the CQC to inspect the Taunton-based PRAS on 29 April.
Amanda Williams, CQC's head of hospital inspection for the south, said the regulator had since taken "urgent action to suspend the registration" of PRAS.
She said: "We took this action because we believe if we didn't, people using the service may be exposed to the risk of harm.
"Premier Rescue Ambulance Services Limited has the right to appeal and further information will be published by CQC when we are able to do so."
Norfolk and Suffolk NHS Foundation Trust said last year that following Mrs Copeland's death it would no longer allow "frail and older" patients to be sent out of the county for care.