More than 150 taxis were sent to 999 emergency calls instead of ambulances to pick up patients in the South West last year, it has been revealed.
Andy Burnham, Labour's Shadow Health Secretary, said the South Western Ambulance Service (SWAS) has seen a 350% rise in the number of taxis attending 999 calls.
The figures were obtained by the party via a Freedom of Information request showing 158 taxis attended 999 calls in the region in 2012/13, up from 35 occasions in 2009/10.
Mr Burnham also claimed other ambulance services are using police cars and retained firefighters to attend calls.
SWAS is a giant single organisation covering more than 10,000 square miles. Last year it was enlarged following its acquisition of neighbouring Great Western Ambulance Service.
In addition to Devon, Dorset, Somerset, Cornwall and the Isles of Scilly, the area now covered by the service now includes Gloucestershire, Wiltshire and the former county of Avon.
Mr Burnham claimed his evidence showed the deepening crisis in accident and emergency (A&E) wards as ambulances become "trapped" at A&Es and unable to handover patients.
He also urged Health Secretary Jeremy Hunt to take action now to avoid the ambulance hold-ups "engulfing" other emergency services.
But Mr Hunt accused his shadow of talking up a crisis that is not happening and said the coalition was hitting its targets, unlike the last Labour administration when Mr Burnham was health secretary.
Mr Burnham told Mr Hunt during health questions: "Today I want to put to you new evidence that the A&E crisis is deepening and having a serious knock-on effect on ambulance services.
"Information from police forces reveals that police cars having to ferry patients to A&E is far more widespread than people realise and in some areas happening on a daily basis.
"One ambulance service is now using retained firefighters to attend calls but this is how bad things have got – another ambulance service has seen a 350% increase in the number of 999 calls attended by taxis.
"Do you think it's ever acceptable that when a patient dials 999 a taxi turns up instead?"
Mr Hunt replied: "I'm afraid this is utterly irresponsible. We are hitting our A&E target, we are hitting our ambulance standard. When you were health secretary you missed the ambulance standard for October, November, December and January.
"What you are doing is trying to talk up a crisis that isn't happening and you should think about people on the front line and just for once put patients before politics."