Brown's 'lack of respect' – by right-to-die campaigner Debbie Purdy

Mr Brown said changing the law would run the risk of putting vulnerable people under pressure to end their lives and result in an erosion of trust in the caring professions.

But Ms Purdy, from Undercliffe in Bradford, said she believes changing the law will actually save lives by allowing open discussion.

Mr Brown's comments come as Keir Starmer QC, the Director of Public Prosecutions, prepares to publish full guidance tomorrow on when prosecutions for assisted suicide should be brought.

Mr Starmer was forced to act by a House of Lords judgment in the case of Ms Purdy, a multiple sclerosis sufferer who wanted to know if her husband would be prosecuted for helping her end her life at the Dignitas clinic in Switzerland.

Writing in the Daily Telegraph, the Prime Minister said: "Let us be clear: death as an option and an entitlement, via whatever bureaucratic processes a change in the law on assisted suicide might devise, would fundamentally change the way we think about death.

"The risk of pressures - however subtle - on the frail and the vulnerable, who may for example feel their existences burdensome to others, cannot ever be entirely excluded."

He added: "The inevitable erosion of trust in the caring professions - if they were in a position to end life - would be to lose something very precious."

Ms Purdy suggested Mr Brown was giving his personal view rather than speaking as a representative of the British people.

She said: "To have a Prime Minister who says actually I don't care if 95% of the population think we should find a law and discuss whether it's possible or not... I think it shows a lack of respect for the British people.

"If the Dutch and the Americans can handle a law, why doesn't he think the British people are capable of the same thing? Does he have that little respect for us?

"He doesn't trust us not to kill vulnerable people in our families.

"I have more faith in the British public than Gordon Brown appears to have which is quite sad really, seeing as he's the Prime Minister."

Ms Purdy continued: "In Oregon and in Holland the relationship between doctors and patients is actually really strong, partly because people know they are not going to be abandoned at the most difficult time in their illness - that's what happens in the UK."

She said a law could allow discussion, perhaps in the form of a tribunal, to find a solution, with assisted dying as a last resort.

She said: "I honestly believe changing the law will save lives.

"It's like having a safety net when you walk on the high wire.

"It's there just in case you fall.

"The majority of doctors and nurses will welcome that because it will give clear guidelines that they don't have to abandon their patients at the worst moment."

Mr Brown said Mr Starmer should be free to clarify the legal guidelines on assisted suicide but Parliament should not alter the law.

He added: "I believe that a duty of government is to minimise the fear of dying badly."

Ms Purdy said she agreed with this sentiment "completely" but that by refusing to allow assisted dying Mr Brown was "doing the opposite".

Ms Purdy took her case to the highest court in the country after the High Court and Court of Appeal held that it was for Parliament, not the courts, to change the law.

She wanted to know what would happen to her Cuban husband, Omar Puente, if he helped her travel abroad to end her life.

The Law Lords agreed that changes were a matter for Parliament but upheld Ms Purdy's argument that the DPP should put in writing the factors he regarded as relevant in deciding whether or not to prosecute.

Mr Starmer outlined interim guidelines last September.

Factors in favour of a prosecution included that the victim was under 18 and did not ask personally "on his or her own initiative for the assistance of the suspect".

Factors against taking legal action included that the victim had a "clear, settled and informed wish to commit suicide".