A bid to boost organ donation by allowing a presumption of consent unless people actively opted out of the programme has been rejected by MPs.
All people would be considered donors unless they objected
The current system only allows organs to be removed if people carry a donor card or families agree a donation.
Supporters of the proposals say they would vastly increase the numbers of organs available for transplants, but critics insist there is no proof.
Opponents say presumed consent is no consent at all.
The government told Labour MPs to vote against the amendment to the new Human Tissue Bill.
But 19 voted against the whip, including two ex-cabinet ministers - Clare Short and Robin Cook.
Opinion polls suggest the majority of the public would agree to be donors, but campaigners say bereaved relatives are increasingly refusing to give consent.
MPs rejected the change by 307 votes to 60.
Health Secretary John Reid defended Labour's decision to tell its MPs how to vote.
"This decision over one's own body is for the conscience - the conscience of individual citizens in this country," he said.
"It is not for this Parliament, by free vote or other vote, to impose upon them a requisition of their bodies after death for the state."
Health Minster Rosie Winterton said the government's consultations showed people did not want consent to be presumed.
"People should give their consent if they want to give parts of their body for research or for
transplant," she said.
"If people donate, it is actually a gift to society."
'Give us hope'
Ms Winterton said the rates of transplant donations had plummeted in France after an outcry against the presumed consent system.
That anger was prompted by a case where children's corneas were taken without their parents' agreement, she said.
But Julie King, who has been on dialysis for 12 years waiting for a kidney transplant, said the change could make a huge difference.
"Not only will it hopefully allow more organs, it will give people hope that there is a chance to get an organ," she said.
Labour backbencher Stephen Pound said the government's opposition to the move was
The Tories and Liberal Democrats gave their MPs a free vote on the issue.
Lib Dem MP Evan Harris, who spearheaded the attempt to change the law, accused the government of being "extremely dishonest" in claiming there was evidence to back its view.
He vowed to fight on saying: "We owe it to those who are dying on waiting lists."
"While I am disappointed that the government dragooned its backbenchers on a three-line whip to oppose this, it was encouraging there was
extensive cross-party support nonetheless."
Ministers had already modified the Human Tissue Bill following fears it would compromise medical research.
Scientists were concerned the Bill would have outlawed the use of any human tissue for research without a patient's explicit consent.
A change means scientists can assume tissue taken from living patients can be used for research.