Hospitals say they have been hit by a 'frightening' shortage of locum staff because of changes to junior doctors' training.
Modernising Medical Careers has slashed the number of doctors willing to work short-term by up to a fifth, leaving hospitals with too few experienced doctors, HSJ has been told.
The undersupply means agencies are hiking up their fees, forcing trusts to spend more cash on temporary staff, experts say.
They claim that the problem is caused by the move under MMC to a 'big bang' changeover, with all training posts across the country starting and finishing on the same date in August.
Previously, posts started and ended at different times of the year, meaning doctors could carry out locum work between jobs.
London deanery programme director Dr Richard Marks said: 'This is a really big problem that no-one's really thought through.
'Three months ago everyone was talking about doctors without jobs but now there are jobs with no doctors to fill them.
'It's really frightening to be involved in because all the trusts are suddenly realising it's a problem. Availability is going down by 20 per cent and agencies are being forced to close.'
Worthing and Southlands Hospitals trust director of medical education Dr Gordon Caldwell blamed the problem on the disillusion experienced when 30,000 junior doctors were fighting for 23,000 specialist training posts this year under MMC.
This encouraged many of them to seek work abroad, or quit the medical profession altogether, he claimed.
And a failed attempt by the Department of Health to stop international medical graduates from outside the European Economic Area applying to training posts made matters worse.
'A lot of locums are international graduates but because of the extremely shoddy way the NHS treated them, they don't want to work here,' he said.
'Normally it's not difficult to get a locum - we get them in so the hospital will be safe. But since the autumn months we've had great difficulties in getting cover.'
Dr Caldwell said that the shortage of locums had encouraged agencies to charge 'astronomically expensive' rates.
A senior medical human resources officer at an acute trust, who did not want to be named, agreed.
The trust was increasingly having to recruit from agencies with which it had no service level agreement. They were charging up to£11 an hour more for a junior doctor locum than an internal member of staff would be paid.
The HR officer said: 'In the past we've had no trouble filling shifts, but we're finding that the agencies haven't got anybody out there and the ones they do have aren't up to the grade.'
Imraan Ladak, chief executive of Milton Keynes-based DRC Locums, said demand for junior doctors had been 'very busy' over the past year.
However, NHS Employers deputy director Sian Thomas said the issue of a shortage of locums had not yet come to her attention.