British hospitals are "running out of surgeons" as they try to prepare for new rules that will cut doctors' working hours, leading medics warn.
The Association of Surgeons in Training surveyed 1,096 trainee surgeons - and 90% said they were working more than the maximum of 58 hours a week.
Under the European Working Time Directive, due to come in this August, this will be cut to 48 hours.
The Royal College of Surgeons warns that staff levels may be cut too much.
Surgeons want to be able to opt out from the directive.
They also say that, because of the new rules, there is less overlap between doctors' shifts, so handovers are more rushed - and unsafe.
John Black, president of the Royal College of Surgeons said: "This is a worry for today and tomorrow.
"There are simply not the surgeons in the UK to fill the gaps when every doctor's hours are cut to a 48 hours per week maximum.
"Trainees are telling the college they cannot gain enough experience to progress on the shortened hours."
"Do we want patients of the future to be treated by a group of highly skilled and experienced surgeons, or be passed around a wider group of lower skilled surgeons with less experience?"
The European Working Time Directive first came into force in the UK in October 1998.
It is meant to protect workers from exploitation and sets a limit of an average 48-hour week, though workers can choose to do more than that if they want to.
To date, doctors have not been covered by the directive and have been able to work up to 58 hours a week, including time on-call.
The survey showed significant under-reporting of hours worked by trainees as NHS Trusts struggle to meet the new restrictions.
It found only 25% of surgeons think their human resource departments accurately reflect their actual working hours.
And 85% come in to do surgery on their days off.
More than two-thirds reported a deterioration in the quality of training and operative skills as a result of the new working patterns.
Alastair Henderson of NHS Employers, which represents hospital trusts, disagrees with the surgeons' call for a blanket opt-out for all the specialist surgical services.
He said: "We believe that increasing junior surgeons' hours would be a backward step."
"We recognise, however, that there are a small number of services for which compliance may not be possible by August 2009.
"In those circumstances arrangements which offer a derogation of up to 52 hours work per week for a limited time are being considered, subject to EU approval."
The Department of Health said it welcomed the survey.
"The NHS is planning for all doctors in training to be working a 48-hour week from 2009 and half already do so. A few hospitals have implemented the maximum 48-hour week across all rotas a year early, including East Sussex and Wigan and Leigh NHS trusts.
"We are monitoring the situation as some smaller specialities and isolated hospitals may find meeting the deadline more challenging."
Shadow health secretary Andrew Lansley said: "I warned the government over four years ago about the problems arising from the European Working Time Directive.
"Junior doctors should never be overstretched but the lack of flexibility means they are not getting the exposure that they want and that patients need to deliver a world-class health service."
But the BMA chairman, Dr Hamish Meldrum, said the NHS has had more than 10 years to prepare for the reduction in junior doctors' working hours.
"The problem is not the directive itself," he said.
"It is the complacency of some trusts in not making the changes needed in working practices to comply with the legislation."