Large pay bonuses cannot be taken away from doctors, even if their performance deteriorates, because of a loophole in the system, the BBC has found.
It means more than half of the 36,000 consultants in England now get what are effectively "lifetime" awards on top of the average £89,400 basic pay.
The scheme, which is under review, is worth more than £75,000 a year to the best-performing consultants.
But doctors defended the system, saying it ensured excellence was rewarded.
The bonus scheme dates back to 1948 when the NHS was created. In England, there are 16 different levels, ranging from £2,957 to £75,889 a year.
Similar schemes operate elsewhere in the UK, although only a small number of doctors receive the awards.
During the summer, all four governments agreed to a review of the bonuses amid concerns about the costs.
In England, the cost of the awards topped £200m last year.
But news of the pay protection clause has added weight to calls for the scheme to be scrapped.
According to latest figures, 19,892 consultants in England are paid the bonuses.
To apply for an award, consultants nominate themselves and are asked to provide details of excellent performance and innovation in terms of clinical care, research and training.
The awards are reassessed every five years, but critics said the loophole had created a culture where that checking process was effectively obsolete.
In fact, evidence to a government review by the Advisory Committee on Clinical Excellence Awards - the body which oversees the top payouts - even acknowledges that reassessments have not always taken place.
During the four years between 2006 to 2009, just seven of the top awards worth over £35,484 were withdrawn.
In 2010, the committee chased up those doctors who had not been taking part in the reassessment process.
However, because of the pay protection clause all these doctors have continued to get the payouts even though the 'bonuses' have been formally withdrawn from them.
Those who have had their awards withdrawn do not receive annual pay rises so the NHS can start to claw back some of the money, but as pay is currently frozen, that is having little impact.
It is not known how many of the local awards have been withdrawn, but according to those who have helped administer the scheme the bonuses come with a virtual "lifetime" guarantee.
Professor Alan Maynard, an expert in health policy at York University, was chairman of a local NHS trust for 12 years during which time he sat on the committee that handed out the awards.
He said: "They never get stopped, once they have them they have them for their lifetime. The system needs completely changing.
"The applicants provide very little information, but you can't spend the money on anything else as it is earmarked for these awards. I would have preferred to spend it on providing more care."
He said the evidence for performance-related pay was questionable anyway, but if there was to be an incentives scheme it should be much tougher.
Professor John Appleby, chief economist at the King's Fund, agreed.
"I think they are out of step with how the NHS should be paying staff. They should be abolished."
But Dr Paul Flynn, of the British Medical Association consultants' committee, defended the scheme.
"It is an integral part of the pay structure for consultants. It is only right that those who go over and above what is expected and do the best job get their performance rewarded."
He said the BMA would be willing to engage with the government to make sure the system was "transparent, fair and responsive".
But he said pay protection was important as doctors needed "security of income" and so that the bonuses "engaged and motivated, but not distracted" them.
A Department of Health spokeswoman said there were "anomalies" in the system and that was why it was being reviewed.
She added: "In future we want to see a much tougher approach, including withdrawing them from people who no longer display the quality of work that would merit an award now."
The review is being carried out by independent Doctors' and Dentists' Review Body and is due to report next summer.