Half of Scotland's junior doctors are working hours which will breach new European rules, leading to warnings over patient safety.

The number of hours young doctors are allowed to spend on hospital wards will be cut to 48 per week next year - and health boards who break the limit could face a fine and legal action.

With 12 months to go, a request by The Herald under the Freedom of Information Act has revealed more than 2500 doctors in Scotland are employed on rotas which exceed this limit - even though the NHS has known about the deadline for reducing hours for eight years. Only one of the 11 mainland health boards was able to produce an action plan to deal with the change.

In some health board areas more than 70% of juniors are working longer hours and in six regions the proportion is more than 60%. The longest working weeks exceed the limit by almost 10 hours.

Dr Alan Robertson, chairman of the British Medical Association's Scottish Junior Doctors' Committee, warned there could be chaos as hospitals strive to meet the deadline.

He said: "The European Working Time Directive (EWTD) is health and safety legislation and it needs to be implemented. If you look at other industries, for example where people fly planes, there are limits to what staff can do and we worry about how people can react to things when they are very tired."

Ross Finnie, Shadow Health Secretary for the LibDems, said the revelations are "appalling".

"Exceeding the Working Time Directive can only compromise patient safety," he said. "Health boards have absolutely no excuse for any failure to implement it."

The EWTD, which became part of British law in 1998, has been implemented gradually. An interim 58-hour week applied from August 2004 and fell to 56 hours in August 2007, but doctors have said that even complying with the current interim target has been difficult.

In the past, health boards have cited the EWTD as a reason for centralising hospital services. It is understood recruiting nurses to take on some of the doctors' work and cutting the number of juniors available in hospitals at night are among the more recent proposals for meeting the deadline.

Dr Robertson said the BMA was concerned the training junior doctors need to become consultants would be sacrificed in a rush to cut working hours.

He said: "In the short term it will not be an issue because people will have enough experience to get by. In the long term it means you are not preparing the workforce for the future."

Junior doctors who want to become surgeons or enter other fields where they perform procedures - such as cardiology - have long been concerned about whether the 48-hour restriction will give them enough exposure to theatre to hone their skills.

Dr Robertson said he was aware of these concerns and wanted standards to be maintained. But rather than working more than 48 hours a week, he said, extending the training period may have to be considered.

The Scottish Government said it would expect all boards to take the appropriate steps to comply with the EU directive and part of that would be for them to come forward with a compliance plan.

Health Minister Shona Robison said: "All NHS Boards in Scotland are expected to put in place arrangements to comply with the working time regulations due to come into effect this time next year.

"The Scottish Government health directorate continues to work with NHS boards to provide advice and support for their implementation of working time regulations."