PlayThe Prime Minister could face an embarrassing setback over plans to make everyone a potential organ donor, unless they opt out.
Gordon Brown has said thousands of lives could be saved by a system where people are automatically placed on the organ donor register.
But an official review now looks set to stop a change in the law - which will come as a crushing blow to the thousands of patients currently waiting for transplants.
According to reports, the Organ Donation Taskforce, set up by the Government to help increase the number of donors, will oppose the change next week.
Earlier, an influential committee of peers found no "convincing case" for an opt-out system of organ donation in the UK, the Lords was told earlier.
Crossbencher Baroness Howarth of Breckland, who led an investigation into the supply of donor organs in the EU, said the Government's top priority should be a restructuring of existing transplant services.
Her remarks came as the Government task force set up to examine the situation was reported to be set to reject any change to a system of "presumed consent".
Lady Howarth said there was a "severe shortage" of organs available for transplant in the UK and warned this was a "serious public health problem".
She led an inquiry by the Lords European Union Committee into transplant services across Europe.
Lady Howarth said: "There is a severe shortage of organs available for transplant, both in the UK and across the European Union. This is a serious public health problem which has significant human and economic costs."
The UK's level of organ donation is "substantially" behind the overall EU average rate at around 12.8 donations per million people.
Spain has seen an increase in the number of donated organs from 14 per million people in 1989 to 35 per million but the committee was told that was down to improved training and organisation rather than the country's presumed consent law.
© Independent Television News Limited 2008. All rights reserved.