The couple, from Bath in western England, both died at the Dignitas clinic in Zurich on 27 February, the family said.

Peter Duff, 80, had colon and liver cancer, and his 70-year-old wife, Penelope, suffered from a rare form of the disease, gastrointestinal stromal tumour, or Gist, for years.

"Peter and Penny Duff passed away peacefully together in Zurich after a long battle against their terminal cancer on the 27th February," the family said in a statement issued late Thursday.

"Penny had fought a rare cancer, Gist, since 1992 and Peter’s colon cancer had spread to his liver.

"Their decision in no way reflected on the wonderful and humbling care they have received from their consultant, doctors and nurses, for which the family, and they, were so appreciative."

The couple kept their plans secret from all but their close family, although their daughter, Helena Conibear, declined to say whether she or any other relatives accompanied the Duffs to Zurich.

A neighbour, David Keeling, 64, said the couple left their friends in Bath with the impression that they were moving to their country home.

"They certainly didn’t tell anyone here they were going to Switzerland, and that has come as a complete shock," he told reporters.

Dignitas has become a destination for people worldwide who are terminally ill and want to die, but need help to end their lives. Assisted suicide is legal in Switzerland, unlike in Britain.

But the issue raises questions over ethics and legality, in particular whether the relatives of those who die at Dignitas could or should be prosecuted in their home countries for their involvement.

AFP / Expatica