Campaigners last night renewed calls for a change in the law after a British woman suffering from a rare brain disease committed assisted suicide in Switzerland.

The day before her 67th birthday, retired doctor Anne Turner died with the help of medics from the controversial Dignitas clinic.

Dr Turner was suffering from progressive supranuclear palsy, or PSP, an incurable degenerative disease.

After drinking a lethal dose of barbiturates, she died at 12.35pm at a flat in the suburbs of Zurich, surrounded by her three adult children.

Her son, Edward, 39, said after his mother's death: "We are very thankful that her suffering is over.

"We will respect her choice and we will miss her very much. She was ready to go and that makes it all the easier for us."

Dr Turner was in the relatively early stages of the disease and was still able to walk unaided, eat and communicate.

Dr Turner first noticed symptoms in January 2003.

She said: "I feel strongly that assisted suicide should become legal in the UK.

"If I knew that when things got so bad, I would be able to request assisted suicide in Britain, then I would not have to die before I am completely ready to do so."

She said she attempted to commit suicide by suffocation at her home in Bath last October, but failed.

Asked if she was certain she was doing the right thing, Dr Turner said: "Absolutely. I am resolute. I do not want to end up like Dudley Moore - he couldn't walk, talk or even blink at the end, and I certainly don't want that."

Dr Turner survived breast cancer after undergoing a mastectomy in 2004.

Her husband, Jack, a GP, died from multiple systems atrophy, a degenerative disease, in September 2002, and his younger brother died of motor neurone disease a few months earlier.

Dr Turner, who ran a family planning clinic, said: "My three children all support my decision, especially as we have all seen the effect of a very similar illness in my husband - his terrible suffering, loss of dignity and his long slow demise.

"I don't think death has ever held any fear for me.

"When I was 18, I thought I was going to die.

"I was bitten by an adder in Kent.

"I haven't got faith, I'm a humanist. I've always felt that dying is like going to sleep."

Delivering her message to the Government on Britain's ban on assisted suicide, Dr Turner said: "Please allow it to be done legally in this country so that it is not confined to people such as myself with the support and money to be able to travel abroad and do it.

"It has been an awful business."

Her decision to commit assisted suicide while still only partially disabled has re-ignited the debate over Britain's laws on assisted dying and euthanasia.

Deborah Annetts, chief executive of Dignity in Dying, formerly known as the Voluntary Euthanasia Society, described Dr Turner's case as "truly heart-breaking".

"The Government must make time in Parliament for the Assisted Dying for the Terminally Ill Bill," she said.

"If this Bill had been law, Anne would not have been forced to go to Zurich while she was still able to travel, for help to die. She would be alive today."

Dr Turner was accompanied to Switzerland by Edward and daughters Sophie Pandit, 41, an actor, and Jessica Wharton, 37, a legal executive.

After her mother's death, Sophie said: "I was very glad it was peaceful.

"I am so relieved that she is not suffering any more, but it is still a terrible shock."

Edward, who is an accountant in London, said the family had been unable to dissuade his mother from suicide.

He said: "Mother announced the diagnosis in December 2004 and said, in the same breath, 'I'm going to kill myself'."

He described the family's final two hours together, saying they chatted, sang some songs and joked.

Edward said the family had enjoyed a Beethoven and Rachmaninov concert after arriving in Switzerland on Sunday, and had taken a boat trip on the city's famous lakes and rivers.

"We bought a bottle of champagne at dinner last night and then had a good cry as we drank," he said.