Patients taken to accident and emergency are waiting for hours outside in ambulances before being admitted.
East Midlands Ambulance Service (EMAS) has the third worst case among Britain’s 12 services with one patient waiting for four hours and 37 minutes.
The longest wait – six hours and 22 minutes – was in Wales.
EMAS has been under fire for being Britain’s worst service for 999 and urgent call responses, but bosses say they are not to blame for long waits outside A&E.
EMAS chief executive Sue Noyes said: “We are working with hospitals across the East Midlands to ensure handover happens as quickly as possible so crews can ‘book clear’ and be available to respond to the next 999 call.”
Hospitals are supposed to accept patients within 15 minutes and an emergency medicine specialist has described the long waiting time figures as “alarming”.
A spokesman for United Lincolnshire Hospitals Trust said: “We recognise that handover times at A&E in hospitals across the East Midlands region have an affect on the response times of the East Midlands Ambulance Service and we are working with EMAS and other partners such as social services and Lincolnshire Community Health Services to ensure we can receive patients into A&E in a timely manner.
“Demand on our A&E departments does fluctuate, and at times a high volume of people come through the departments and are brought to the departments in ambulances.
“When this is the case, we deal with cases based on their urgency and the order in which they arrive, which can occasionally lead to some patients waiting slightly longer to be seen than others.”
The spokesman said the trust had introduced several measures to reduce delays.