A terminally ill Briton has become the latest in a string of assisted suicides at the controversial Swiss euthanasia clinic Dignitas.

John Close, who was suffering from motor neurone disease, flew to Zurich at the weekend and died in the clinic with his family at his bedside.

Mr Close's death comes just a month after a couple from Bedfordshire, Robert and Jennifer Stokes, committed assisted suicide at the Dignitas clinic, despite suffering from chronic rather than terminal illness. Mr Stokes, 59, and his wife, 53, died by drinking the poison pentobarbital sodium.

They were among five people, including another British woman, who arrived in Zurich between March 31 and April 5 to kill themselves.

The clinic, which has been criticised for its methods, is being investigated by the public prosecutor's office in Zurich.

Mr Close, who was 54 and from Milton Keynes, was diagnosed with motor neurone disease in March 2001 but had deteriorated rapidly recently.

His sister, Lesley Close, said: "John decided in January that he would like to end his life at some point because he had MND and had an increasing sense of helplessness and dependence on other people to provide for his everyday needs.

"It was hard, very hard, but it was what John wanted. The staff at Dignitas were so kind, compassionate and humane. He lost the use of his right side and realised the same was happening to his left.

He wanted to go while he was still in control ... It was a safe death.

"If he had tried suicide in this country his concern was that it would have failed and he would have been woken up in hospital by medical staff who had saved him."

Mr Close was one of 500 Britons who have become members of Dignitas since January, when 74-year-old Reginald Crew, also a motor neurone disease sufferer, became the second Briton to die at the Dignitas clinic.

But the Swiss authorities have become increasingly embarrassed by the number of "suicide tourists" travelling to Zurich. Dignitas has aided the deaths of more than 100 people from around the world.

Vivienne Nathanson, head of science and ethics at the British Medical Association, which opposes euthanasia, said after Mr and Mrs Stokes' deaths: "It certainly strengthens my view that it is very difficult to write the law so tightly that you don't get unexpected consequences. That has to give everyone cause for concern, whether they are for or against."