It is illegal to take organs without consent
Organs may have been removed from deceased people without their consent after a data-handling error by the NHS.
The blunder meant 800,000 people on the UK donor register may have had their wishes about the use of organs for transplant wrongly recorded.
The Sunday Telegraph reported that 45 of them have now died - and 20 families let organs of relatives be taken based on incorrectly stored information.
NHS Blood and Transplant said it was urgently investigating.
Many donors give consent for some organs to be used for transplant but not others, such as eyes.
But the details of many donors' preferences were accidentally deleted in 1999.
It first came to light in 2009 when NHS Blood and Transplant wrote to donors, reiterating what they had agreed to donate.
But many wrote back saying the information was incorrect.
Joyce Robins of pressure group Patient Concern told the Sunday Telegraph: "This government has got an absolutely dreadful record when it comes to data, but it is horrific that such sensitive details were handled in such a careless way."
NHS Blood and Transplant has since corrected 400,000 flawed records - but hundreds of thousands of people must now be contacted to confirm which organs may be taken.
Until consent is given from those affected, no organs will be removed.
It is against the law to take organs from the dead without their prior consent, or that of their family after death.
A spokeswoman for NHS Blood and Transplant said: "We are aware of issues with the records with a small proportion of the people who signed up to the NHS organ donor register.
"We are taking it very seriously and are urgently investigating the situation.
"Our priority is in ensuring that the families of those who may have been affected are contacted."
Liberal Democrat health spokesman Norman Lamb described the data error as "a shocking failure of proper controls".
"The Liberals Democrats believe in reforms to provide for assumed consent so as to increase organs available for transplant.
"But for so long as the opt-in consent system is in place it is critical that everybody has confidence in the current system," he said.