The Welsh Ambulance Service has issued a stark warning that its ability to respond to major incidents such as terrorist attacks could be severely hampered by hospital handover delays.

It follows a report being published that highlights the risk of “catastrophic harm” to members of the public if crews are tied up outside emergency departments during serious incidents.

The service has raised concerns after carrying out a mass-casualty simulation exercise, which found it would have failed to provide an adequate response in three out of four scenarios.

The tests were conducted in the wake of the public inquiry into the Manchester Arena bombing, which identified a catalogue of failings by emergency services in the aftermath of the attack.

The ambulance service has questioned the effectiveness of release procedures after its chief executive Jason Killens wrote to health boards across Wales to seek assurances.

The Welsh Government has also said it expects health boards to reduce handover delays “as a priority” in response to the concerns.

The ambulance report states: “If a major incident or mass casualty incident is declared, then there is a risk that the trust cannot provide its pre-determined attendance as set out in the incident response plan and provide an effective, timely, or safe response to patients due to vehicles not being released from hospital sites.”

The report said it would result in “catastrophic harm”.

“The trust is not assured that hospital sites have plans in place that are trained and tested to release ambulances effectively and immediately in the event of an incident declaration,” the report added.

Lee Brooks, executive director of operations at the Welsh Ambulance Service, said it had plans in place to provide an “effective, timely and safe response” to major incidents.

He admitted that hospital handover delays were one of the main factors which could restrict its ability to send crews.

Mr Brooks said: “The consequence of delays to transfer patients from ambulances to emergency departments is well-documented, not just in Wales, but across the UK and beyond.

“Our ability to send a large-scale response to an incident may be hindered if our people and vehicles are not immediately released by emergency departments.

Responding to the concerns, a Welsh Government spokesperson said: “All health boards have urgent and emergency care improvement plans in place, and we expect them to reduce ambulance patient handover delays as a priority over the next six months.”