A move to reverse Britain's law on organ donations goes before MPs today, meaning patients would have to opt out of giving their body parts, rather than choosing to carry a card giving doctors permission as at present.

The issue has already raised controversy, with some Labour MPs complaining that the government has insisted on whipping its backbenchers into opposing the measure, rather than allowing a vote of conscience.

The proposal - an amendment to the government's own human tissue bill - is being introduced by the Liberal Democrats, and both they and the Tories are allowing their MPs a free vote.

But today health minister Rosie Winterton appealed to Labour MPs to reject the proposal.

Despite opinion polls showing public support for the move, she insisted that the French experience revealed a drop off in donations after a similar scheme was introduced, and that the state did not have the right to claim citizens' organs.

She said: "People should give their consent if they want to give parts of their body for research or for transplant. "We believe very firmly that the state does not govern people's bodies, nor do researchers or doctors.

"If people donate, it is actually a gift to society."

Ms Winterton said: "In France they had a system of presumed consent, because of one case where children's corneas were taken without their parents' consent.

"Following that outcry, the rates of transplant donation actually plummeted."

The minister told the Today programme "all the evidence" showed that the best way to boost donations was to ask people, not change the legal basis of consent".

"We consulted very widely, including on the issue of presumed consent. It was not what people wanted," she said.

However Labour backbencher Stephen Pound has promised to vote against the measure calling the government's stand "ridiculous" and predicted colleagues will rebel.

The result of the vote is expected late afternoon.