Seriously ill patients are being kept in ambulances outside hospitals for hours so NHS trusts do not miss Government targets.
Thousands of people a year are having to wait outside accident and emergency departments because trusts will not let them in until they can treat them within four hours, in line with a Labour pledge.
The hold-ups mean ambulances are not available to answer fresh 999 calls.
Doctors warned last night that the practice of “patient-stacking” was putting patients’ health at risk.
Figures obtained by the Liberal Democrats show that last year 43,576 patients waited longer than one hour before being let into emergency units.