The number of NHS trusts in England failing to meet target A&E waiting times has more than doubled in the last year, the regulator Monitor has said.
Between April and June, 31 trusts failed to meet their target of seeing patients within four hours of their arrival.
Just 13 trusts missed their waiting times commitment over the same period last year.
The Department of Health said A&Es saw 95% of patients within their targets.
But Monitor raised concerns that services – which usually improve over the spring and summer months – had instead remained challenging.
The regulator’s report looks at the key trends drawn from individual reports of England’s 146 foundation trusts.
It warned that ongoing problems meeting A&E targets may result in “unsatisfactory care” for patients, adding that trusts should prepare for the winter months by putting the right funding in place.
The number of trusts running a financial deficit increased from 36 in the first quarter of 2012/13, to 48 over the same period this year.
During that time, trusts generated £57m less in cost savings than originally planned.
Jason Dorsett, Monitor’s financial risk and reporting director, said: “The increased demand has also prevented trusts from delivering their planned financial savings.
“We expect to see trusts planning now for how the increased demand will impact on their finances, so that they are not storing up trouble for the future.”
‘Severe storms ahead’
Labour responded to the figures by warning there will be “severe storms ahead” for A&E units this winter unless the government addresses issues in staffing and social care.
Shadow health secretary Andy Burnham said: “David Cameron’s ill-judged… re-organisation has placed the NHS in the danger zone.”
A Department of Health spokesperson said the ageing population had put pressure on departments across the UK – with more than a million extra visits made to A&E over the past four years.
The spokesperson said: “A&E departments have been seeing 95% of their patients within four hours since the end of April – as they were before last winter. This is testament to the hard work of staff working throughout the health and care system.”
The government is investing £500m over the next two years to help ensure A&E departments are prepared for the winter.