More than half of trainee doctors are ready to leave the UK if they fail to get a training post, a survey suggests.
Doctors have protested about the application system
The British Medical Association, which carried out the poll of 650 doctors, has asked to meet Health Secretary Patricia Hewitt to review the findings.
There are estimated to be 10,000 more applicants than posts and the BMA wants action to prevent an exodus.
Prime Minister Tony Blair told the BBC there were more doctors chasing jobs because of increased investment.
He told BBC's Breakfast programme: "We doubled the investment in training so whereas for years before we came to power there was a shortage of doctors, and shortage of nurses, now we're in a situation where actually we've got nurses and doctors that we need that are building capacity in the health service."
The Department of Health accepted some trainee doctors went to work abroad, but said the majority returned to the NHS.
The survey is published on the same day that the Conservatives held an opposition debate on the situation.
During the debate, clapping broke out among doctors in the public gallery of the Commons when Tory former minister Peter Bottomley suggested that the Prime Minister should think about using the same system for picking his ministerial health team.
Shadow health secretary Andrew Lansley went on to accuse the government of "chronic mismanagement".
Earlier on Tuesday, Mr Lansley, Lib Dem health spokesman Norman Lamb and Labour backbench MP Ian Gibson all spoke to doctors gathered outside Parliament for a rally organised by doctors' organisation Remedy UK.
Last week, a leaked report showed an employers' organisation was considering options such as working with the charity Voluntary Service Overseas to offer surplus trainee doctors the opportunity to go abroad.
However, the most likely option is that doctors who do not get training posts will be offered a service grade NHS job - which does not include any training.
But the BMA's survey found two thirds of those polled would not consider this kind of job.
It also found that 4.5% of the doctors surveyed have already had offers of posts overseas confirmed.
And 39% said they would seek medical employment outside the NHS, while 44% said they might leave medicine altogether.
The BMA wants a guarantee from the Department of Health that no junior doctor will lose out on training as a result of the online application process (MTAS) or competition for posts.
Dr Jo Hilborne, chairman of the BMA's Junior Doctors Committee, says: "The NHS could lose thousands of its best young doctors simply because of poor planning. This is not acceptable.
"It's unfair on them, it's unfair on their patients, and it's unfair on the taxpayers who've funded their training."
'Many options open'
She added: "These changes have caused anxiety on a massive scale, and we are concerned about their impact on patient care as well as doctors' morale.
Under the new system, doctors should achieve consultant level in 11 years instead of 14
The online application process MTAS (Medical Training Application Service) has been heavily criticised
Doctors cited badly designed forms and poor selection methods and warned the best candidates would miss out on jobs
An independent review panel has already recommended a number of changes to MTAS
"We want to discuss ways of addressing this with the health secretary."
Matt Jamison-Evans, of Remedy UK said: "Junior doctors want to be moving forward with their skills.
"People will either leave the profession, or will leave the country and get training somewhere else."
But a Department of Health spokeswoman said: "There are many options open to applicants who do not secure a training place, including trust grade posts in the NHS, locum work, or spending a period of time working outside the NHS.
"However, it's not unusual for doctors to either work abroad or travel and Australia and New Zealand are favourite destinations.
"The majority of those who go abroad come back to England to continue their careers in the NHS, enriched by their overseas experiences," the spokesman said.