The son of a Bath doctor who ended her life at a Swiss clinic has accused the Government of "moral cowardice" over its stance on voluntary euthanasia.

Edward Turner's attack on Ministers came the day after it was revealed Peter and Penelope Duff, also from Bath, had taken the decision to travel to the euthanasia clinic Dignitas to die.

Mr Turner himself travelled to Switzerland three years ago as his mother Dr Anne Turner took the decision to die in an assisted suicide.

Accountant Mr Turner is now a director of Dignity in Dying, a pressure group calling for a change in the law to allow voluntary euthanasia.

His mother, a family planning specialist, died on the day before her 67th birthday in 2006 while suffering from progressive supranuclear palsy, an incurable degenerative disease which also killed actor Dudley Moore.

Dr Turner flew to Switzerland while she was still able to walk unaided, eat and communicate, and before her death said the law should be changed so terminally ill patients did not have to die before they were ready, by being forced to travel abroad while still able to do so.

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

Mr Turner said he could fully understand the painful decisions the Duffs had faced and why they chose to end their lives.

"It's very sad that they had to leave this country in order to die. It's not natural or normal," said Mr Turner.

"I would have hoped that by now we could have accepted that assisted dying can be done sensitively and with dignity.

"They were mentally competent adults who were well able to come to a rational choice, to be able to say enough is enough, we don't want to suffer any more.

"It's not for any of us to tell them what's right and what's wrong – no one is better placed to judge."

Mr Turner said the Government could have used the Coroners and Justice Bill to allow voluntary euthanasia but had actually made it more likely that people might be prosecuted over the issue.

"The Government has shown moral cowardice over this," he added.

Bath MP Don Foster, however, said he was not in favour of any change in the law.

The Liberal Democrat said the Duffs' case was "an absolute tragedy" and that the issue posed a "huge dilemma".

He said there was a need for huge improvements in the palliative care system for people with diseases such as cancer.

"It's a disgrace that the hospice movement gets little or no Government support.

"We need to do much more about end of life support.

"It strikes me that the real danger of legalising assisted suicide is that you will have some people who feel they are such a burden to friends and family that they feel pressurised into doing it."

Dr John Troyer, a researcher in Death and Society at the University of Bath, yesterday called for the Government to consider allowing the terminally ill to choose when to die. He said of the Duffs: "This is not an isolated case – instead it's indicative of a larger trend that will become more and more common. The question of whether terminally ill people should have the right to choose when to die isn't going to go away – and Parliament can either choose to address it or not. The majority of the British public think patients should be able to decide for themselves and that they should have the choice available here in the UK rather than having to travel to Switzerland. The US states of Washington and Oregon have passed laws permitting assisted suicide. I believe that similar laws would be workable here in the UK too."

A spokesman for Dorset police revealed the force was not conducting an investigation into the assisted suicides of the Duffs.

He said: ''With regard to the reported deaths of Peter and Penelope Duff in Switzerland, neither Dorset police nor the two Dorset coroners are making any investigation into the circumstances." Avon and Somerset police also said it would not be investigating.

Jo Cartwright, spokeswoman for Dying in Dignity, believes it is ''very unlikely" there will be an inquest or police investigation. She said: ''The rules in Switzerland mean the bodies of Dignitas clients are cremated and that makes carrying out an inquest difficult. Furthermore, before the death extensive medical records and forms are filled out which negates the need for an inquiry.

"In terms of a police investigation, sometimes people who have accompanied someone to Switzerland go to the police and say 'this is what I have done'. In other cases the police are waiting for them when they get back. However, in this case an investigation seems very unlikely because so much has been said publicly."