A cross-party group of MPs failed last night in an attempt to increase the number of donated organs available for transplant.

A three-line whip imposed by the government ensured that the MPs' amendment to the human tissue bill - to replace donor cards with an opt-out system - was defeated by 307 votes to 60, a government majority of 247.

Evan Harris, a former doctor and LibDem MP who proposed the amendment, said that an opt-out system "would tackle the real cause of low rates of donation". It would allow organs to be used unless a dead person had ruled out donating part of their body.

He added: "At the moment relatives have to guess. They play safe, which means that other people suffer because those organs aren't available, when we know that 90% of people would support it."

Labour MP Stephen Pound asked why they would not be allowed a free vote on the amendment. Rosie Winterton, the health minister, said: "The whole basis of the bill is of informed consent. To remove one part of that - the bit referring to transplantation - from the wider bill would go against everything we have said in response to the inquiries at Alder Hay, [and] at Bristol."

The health secretary, John Reid, said: "It is not the role of this parliament to remove from individuals ... the right to exercise their own choice. That is the sole reason why there is not a free vote, because in so doing we would not be extending the power of people in this country to exercise their conscience. We would be taking it off them by assuming consent."