Some surgeons are working unpaid overtime to ensure continuity of care
Patients' lives are being jeopardised by European rules that cut the working hours of doctors, experts say.
The Royal College of Surgeons says the 48-hour limit on the working week has left hospitals overstretched.
Two-thirds of the 900 NHS surgeons polled said quality of care had worsened since the European Working Time Directive started in August.
The Department of Health said it had received no evidence that the directive was not working.
The rules are designed to stop doctors working the 80-hour weeks that were commonplace under the old system.
But the RCS has long warned that the directive will compromise patient safety. Now it says it has proof that this is the case.
According to the survey, 62% of surgeons said they were not complying with a 48-hour week and half of consultants said compliance with the European regulation had been achieved at the expense of patient safety.
RCS President John Black said: "Throughout this affair the call from the Department of Health has been that this legislation is about making patients safer.
"We now have a clear message from the front line that patient care is being made significantly less safe through systems that lead to poor continuity of care, the loss of teams and 'wildcat' closure of services."
He said trainee surgeons across the country were staying on unpaid after the hours limit because they wanted to see through care for patients.
And they were taking on additional paid locum work in the hope of gaining the training opportunities they could not get in their formal working week, he added.
A Department of Health spokeswoman said the overriding priority would continue to be ensuring that patients experienced high-quality, safe and effective care in the NHS.
"There is no evidence of harm being caused to patients.
"In fact the independent regulator responsible for junior doctor training said there is evidence the European Working Time Directive improves patient safety but little evidence that it reduces the quality of training."
Patient safety charity Action against Medical Accidents said: "If the feedback from the Royal College of Surgeons is true, and we have no reason to believe that it isn't, this is extremely worrying and, frankly, scandalous.
"There can be no excuse for allowing patient safety to be compromised and patients to be harmed needlessly."
It said every NHS trust ought to be able to produce evidence of what steps they had taken to ensure safety while implementing the changes and these should be independently reviewed.