Princess Margaret's Sunday afternoon television habits have rarely elicited comment, or indeed interest, until now. But there we were being told by the BBC's One O'Clock News this week that the princess and her lady-in-waiting, Lady Glenconner, had settled down together to watch the Antiques Roadshow at Sandringham last Sunday.

The royal younger sister, so the story goes, has been an enthusiastic socialite for much of her adult life, at times relying on cigarettes and Famous Grouse whisky to get her through rocky romances. But the Antiques Roadshow portrait, ordinary as it was, seemed such a long way from the hedonistic days of the 1970s when the princess was setting the benchmark for royal bad behaviour.

As she is now, frail and ill and receiving perhaps the most expensive medical care at the private King Edward VII hospital in London for what may be the effects of a second stroke, Princess Margaret is a shadow of the former sparkling socialite. And from a discreet distance, the media monitors every aspect of her life and health.

Queen Elizabeth's sense of triumph that her sister was able to eat some food at the weekend - a BBC royal correspondent told viewers she managed to eat a jam tart - was a result of growing concern about Princess Margaret's health. Her friends have spoken of the princess's depression at being ill for so long - although Buckingham Palace has played down these reports - following an incident in 1999 when she badly scalded her feet in a bath.

She has recently had difficulty eating, a condition which developed over the Christmas holidays when the princess spent most of her time in bed at Sandringham, unable to rouse her spirits to attend the annual round of church services with her family.

To be fair to her, the portrait of Margaret jetting off to her holiday home on the Caribbean island of Mustique, whisky in hand, is a little one-sided. In the royal tradition she has patronised many charities and has been an enthusiastic supporter of the arts. However, her position at the centre of a high society troupe of well-bred types and hangers-on partying around the world in the 1960s and 1970s has done little to shake the image of a good-time princess.

As John McEntee, who has a society column in the Daily Express, observed this week, Princess Margaret will probably be remembered not as a frail old woman, but wearing her kaftan "reclining amid a circle of admiring young male acolytes on her beloved Mustique".

Her friends and biographers have suggested that Margaret's love of the high life masked a private sadness. She has long been portrayed in the British media as a sad, tragic figure, always playing second string to her older sister and never recovering from her decision in 1955 to reject Group Captain Peter Townsend in favour of royal duty.

Indeed Margaret's sadness over the affair caused Queen Elizabeth some degree of pain. In Sarah Bradford's book, A Biography of Her Majesty the Queen, she suggested that Queen Elizabeth felt guilty over the Townsend affair and was "desperately sad" when, in 1978, Princess Margaret's marriage to society photographer, Anthony Armstrong-Jones (Lord Snowden) ended in divorce. "Like the rest of Margaret's inner circle, she felt somehow that the unhappy princess's personal well-being was a responsibility on all of them," Bradford wrote.

However, royal and public tolerance of Margaret's excesses had already worn a little thin by the end of the 1970s. The princess and Snowden were leading separate lives and when she was photographed in her swimsuit with the young Roddy Llewellyn on Mustique, Queen Elizabeth agreed it was time for Margaret and Snowden to get on with it and divorce.

It is on her Caribbean hideaway that Princess Margaret has enjoyed the best times of her life, according to friends. The love affair with Mustique began in 1958 when the princess's friend, Colin Tennant, Lord Glenconner, gave her five acres of land on the island, which he then owned. She had a summer house built and with Lord Snowden and Lord Glenconner held A-list parties attended by Mick Jagger and David Bowie. An invitation to Mustique was the highlight of the winter season.

"I had 48 dinners with Princess Margaret over 25 days. I had to take a day off in the middle," Lord Glenconner once said.

The royal rebel, who famously rebuked Fergie over her "disgraceful" behaviour, has determinedly kicked against the royal system while enjoying the fruits it provided.

Princess Margaret's life is full of contradictions - tragedy and excess have walked side by side - and she has played it to the full so far. As the Hon Margaret Rhodes, her cousin, said this week: "She was always able to make people laugh. Since her stroke she has just lost that particular faculty of sparkle."