The government may allow scientists to clone embryos from tissues donated for research without the need for donors' "express" consent, the BBC has learned.
The Lib Dems welcomed the 'sensible compromise'
Health officials say they have accepted that the requirement, currently in the Human Fertilisation and Embryology Bill, would hamper vital research.
The Liberal Democrats said the move was a "very sensible compromise".
But Comment on Reproductive Ethics said research interests were being allowed to override proper consent.
Scientists believe they can learn more about the development of many currently incurable illnesses by creating cloned embryos from diseased tissues.
They say the specific consent requirement would stop them using tissues already donated for general medical research by people who are dead or cannot be contacted.
If the government does drop the requirement from the bill, it is expected to insist stringent safeguards are put in place instead.
'Race against time'
Liberal Democrat health spokesman Dr Evan Harris, who has been campaigning for the change, said: "Scientists would see sometimes decades of work characterising cells wasted if one had to start again with a whole new type of cell or individual cell.
"There's a race against time to find treatments for some of these diseases and of course the job of Parliament is to weigh that against the need for appropriate consent and I think this is a very sensible compromise that the government has agreed to."
The bill, which is designed to reflect both changing public attitudes and scientific advances, has been discussed in the House of Lords this week and is due to enter the Commons in the spring.
On Thursday, it emerged the government was also looking into calls to lift a ban on creating human or human-animal "hybrid" embryos from children dying from genetic diseases.
Campaigners say this could also aid key research.
The current bill would not allow the procedure to take place unless the child was competent to give consent.
But critics argue such children die before being able to give consent.