Nursing staff from a Telford hospital have been accused of using an ambulance as a taxi after a night out.
The Princess Royal Hospital said an inquiry has begun after an allegation said to be from a member of the public.
It was claimed some of the nursing staff got into an ambulance outside The Swan in Ironbridge on Sunday.
The ambulance service has found a crew did provide unauthorised transport to staff but said it was not in operation and returning to base at the time.
Steve Parry, from the service, said its preliminary investigation had also shown patient services were not compromised.
"The episode is most regrettable and disciplinary action is being considered against the crew members concerned," he said.
"The journey was unauthorised and the ambulance crew acknowledge an 'error of judgement' on this occasion."
He said the relationship between ambulance and hospital staff has always been very close but "on this occasion an evening celebration went too far and caused public offence".