The NHS is facing a crisis over medical cover because new EU rules restricting doctors' working hours, which come in this summer, will cost them the work of thousands of junior doctors.

EU restrictions on doctors' working hours limiting them to 58 hours a week, which come in to effect this August, will cost the NHS the equivalent of the work of at least 3,700 junior doctors. According to the British Medical Association (BMA), the loss of manpower will mean that operations will have to be cancelled while queues for treatment will get longer.

Evidence given to a House of Lords committee by the BMA about the impending crisis blames the NHS for failing to take the threat facing the service seriously enough. Dr Simon Eccles, the chairman of the BMA's Junior Doctors Committee, told peers that the NHS could lose the equivalent of 3,700 junior doctors or "some 270,000 hours of time".

"If we continue to require as many doctors present in the hospital available for work as we do at the moment we are in real trouble," he told a House of Lords EU committee. "We have been trying to alert the Department of Health to the scale of the impending disaster for at least three years, as has a number of other bodies."

Ministers are hoping this week to agree a concession on doctors hours after fears were raised that the European Working Time Directive would badly affect NHS service. But sources at the Department of Health say that even if ministers agree, it is unlikely to be implemented by August, when the rules come in.

The change will mean doctors will not be able to stay at work - even if they are resting or on a sleep break - for more than 58 hours a week. Since most junior doctors currently work up to 70 hours a week, this could have a major effect on the level of care offered to sick patients.

The Tories are planning this week to seek reassurances that the UK has resolved the potential crisis in time for the summer. The move follows complaints from the BMA that ministers have failed to grapple with the issue.

Tim Yeo, the shadow Health Secretary, said he planned to raise the looming doctor shortage with ministers at Health Questions this week. "The Government has completely failed to deal with this. They have buried their head in the sand," he said.

Ministers hope to agree an opt-out for Britain at a meeting of European heads of government in Brussels. But earlier this month John Hutton, the health minister, told the House of Lords EU committee that the Government would need to recruit between 6,000 and 12,000 doctors to cover the lost time. "I do not believe that is a sustainable strategy for us to pursue in the timescale that is available and I think that we would struggle to recruit that size of workforce," he said.

Dr Eccles said the BMA was concerned that ministers had not put enough preparations in place to fend off a crisis. "If we continue to try to work at exactly the same way we do now with the new rules in place it will be very difficult to maintain the present levels of service," he said. "Waiting lists will go up and operations will have to be cancelled. There won't be gaps in accident and emergency cover because we always cover emergencies, but there will be cuts in non-emergency operations."