Forty guests gathered shortly before Christmas for an intimate drinks party in an elegant Georgian townhouse overlooking the city of Bath.

The guests, mostly from the philanthropic side of the local arts world, thought that their elderly hosts, Peter and Penelope Duff, were saying thank you after another successful year sponsoring concerts and music festivals in the city. In fact, they were saying goodbye.

A few days after the party the couple packed their bags, closed the white shutters at their five-storey terraced house in Cavendish Crescent for the last time and moved to their cottage in Dorset.

Although their guests didn’t know it, both were terminally ill. Mr Duff, 80, and his wife, 70, had been told by doctors that their cancers had spread and were incurable. Last week, while they still had the strength, they flew to Zurich, in Switzerland. There they checked into the assisted suicide clinic run by Dignitas to end their lives by drinking a cocktail of barbiturates.

The Duffs gave no one outside their immediate family any clue about their intention to take their own lives.

At the party they were the perfect hosts, a little frail but no more than their ages would suggest. Mr Duff, who had made his money in the wine trade, listened but spoke little. When he did speak, say friends, he could be forceful in his views and was clearly the dominant partner.

The couple appeared devoted and were rarely seen apart, venturing out together to attend the many concerts and operatic events they had helped to sponsor. Even in his latter days in Dorset, Mr Duff looked the part of the country squire with his corduroy jacket and Tattersall check shirt. Mrs Duff cut a more gaunt figure, thin and pale-skinned but always elegantly dressed in a long jacket or cape.

John Edwards, treasurer of Iford Arts, which stages exclusive opera productions in an Italian cloister near Bath, said that the Duffs were among his most enthusiastic patrons. As well as donating cash, the couple took an active interest in Iford’s activities.

Mr Edwards, who was among the guests at the farewell party, said: “They always turned up for patrons’ parties and were very involved. For opera productions they would bring a small party and enjoy a meal in the garden before the performance.” He said that Mr Duff was a man with strong views: “It requires considerable guts to say, ‘That’s it, I’m going’, but I suspect he’d been winding down to this over many months.”

Brian Roper, who also donates to arts events in Bath, was another guest at their home. He was shocked to learn that the couple had chosen to end their lives. He said: “We drove past Cavendish Crescent the other day and I said to my wife that it was strange we hadn’t seen the Duffs for a few weeks.

“But we knew that Penny had been having difficulty coping with the stairs because of her illness. They were a very charming couple, very discreet, but thoroughly good company.”

Neither the Duffs’ daughter, Helena Conibear, nor their son Simon Duff, are prepared to discuss the exact circumstances of their parents’ deaths.

Mrs Conibear, whose husband, also called Simon, is the development manager at Poundbury, the Prince of Wales’s model village on the outskirts of Dorchester, said: “This was never intended to be secret, but it is a very serious situation.

“There could be consequences legally, and there are formalities to be resolved with the Swiss authorities. What my parents have done is a beautiful and remarkable thing and until the legal situation is sorted out, I cannot discuss it.”

Friends said that the family was waiting for the death certificates to be signed and for Swiss police to decide whether the deaths required investigation. In the majority of cases they do not, they said, but the formalities had to be observed. Neither Dorset Police nor the Somerset and Avon Constabulary expect to investigate their deaths and there are unlikely to be inquests because the usual practice is for Dignitas to have the bodies cremated.

Although assisting a suicide is an offence still technically punishable by up to 14 years’ imprisonment, a recent ruling by the Appeal Court made it clear that a prosecution in a case like that of the Duffs is extremely unlikely, even if a family member went with them to Switzerland. Dignitas claims to have helped more than 100 Britons to end their lives but there are concerns, even in Switzerland, about the way it operates.

One of the most controversial cases was that of Daniel James, a 23-year-old rugby player who had been paralysed in a training accident and died at Dignitas last September.

However, fears that the unlikelihood of prosecution could have opened the floodgates to large numbers of people determined to end their lives before succumbing to illness or old age were played down by Peter Saunders, campaign director of the pressure group Care Not Killing. He said: “One hundred Britons have ended their lives in Zurich. In the same period there have been three million deaths in this country. That suggests there is not a huge, pent-up demand.”

The Swiss way of dying

1998 The year that the Swiss lawyer Ludwig Minelli founded Dignitas

€4,000 Price of Dignitas assisted suicide

102 Estimated number of Britons who have ended their lives at the clinic

725 Estimated number of Dignitas members in Britain

14 The maximum number of years for which someone can be jailed if convicted of helping a person to commit suicide

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