Britain's accident and emergency crisis is worsening with some patients left in parked ambulances for hours before being admitted to overstretched hospitals, Freedom of Information requests revealed yesterday.

One patient in Wales was forced to wait six hours more than the 15-minute guideline, NHS figures showed.

The delays mean ambulances are kept off the road and unable to deal with new emergencies.

Public-sector union Unison said A&E units were understaffed and unable to cope with increasing numbers of admissions.

But the coalition government is pressing ahead with plans to close more, the union warned.

Unison national officer Hope Daley said: "The A&E crisis is spiralling out of control, the pressures on medical staff are reaching breaking point and sadly this may start costing lives very soon.

"The cuts imposed on the NHS were bound to have a knock-on effect on the ambulance services and patient safety.

"There are simply not enough staff in A&E. This means ambulances can't hand over patients who need vital medical treatment. Things will only get worse as the winter pressures kick in."

Shadow health secretary Andy Burnham accused Prime Minister David Cameron of being "dangerously complacent" about the crisis.

"Ministers are leaving large swathes of the country without adequate ambulance cover," he said.

"People who have faced an anxious wait for an ambulance will be stunned by their complacency.

"David Cameron's fingerprints are all over the A&E crisis. It proves you can't trust the Tories with the NHS."