Record numbers of patients spent more than four hours in accident and emergency units in England in January, figures leaked to the BBC suggest.
During a difficult winter for the NHS, January appears to be the worst performing month since the four-hour target was introduced.
The figures also suggest record numbers of people waited longer than 12 hours for a hospital bed once seen in A&E.
The BMA said the prime minister could no longer “bury her head in the sand”.
And it accused the government of failing to grasp the seriousness of the situation in the NHS.
But a spokesman from the Department of Health said the vast majority of patients were seen and treated quickly, and busy periods in hospitals were supported by an extra £400 million of funding.