With the Caribbean sun blazing down from a clear blue sky, Sir Mark Thatcher was in sparkling form this week at one of the most exclusive addresses in Barbados.

Sipping cocktails at the £1 800-a-night (R22 578) Sandpiper Hotel, Sir Mark, whose fortune was once estimated at £64 million before his dramatic fall from grace over his role in an illegal African coup, was talking about his next big venture.

The son of Margaret Thatcher, Britain’s first woman prime minister, is buying a multi-million-pound property on the island, where he rubs shoulders with the likes of Simon Cowell, Cilla Black and Sir Cliff Richard.

While Sir Mark soaks up the Christmas sun in Barbados for the second year running, his twin sister Carol was getting into the Yuletide spirit in the Swiss resort of Klosters.

Carol, who has been living in Madrid, where she is learning Spanish, is staying with her former partner, ski instructor Marco Grass. They spent Christmas with friends. Last Christmas, Carol was in Italy staying with Lord McAlpine, the former treasurer of the Tory Party, who is a close friend of her mother.

Lady Thatcher, 86, increasingly frail and forgetful after a series of minor strokes, was expected to spend Christmas at home alone, again, with just Kate, her faithful housekeeper and carer, for company.

It is the second year running that the former prime minister, whose political life is the subject of a contentious new film, The Iron Lady, starring Meryl Streep, spent Christmas Day separated from her children in her elegant home in London’s Belgravia.

Although she is forgetful, it will surely have been painfully obvious to her that she was spending the festive period without her children once again.

There is a small artificial Christmas tree, complete with twinkling lights, in one corner of her elegant drawing room. It is here where she spends most of her days listening to music and entertaining the small but loyal group of friends who still call round.

There are Christmas cards on the mantelpiece from her children and closest friends. Hundreds more from well-wishers fill her office at the House of Lords.

There are also countless invitations. But these are increasingly difficult because Lady Thatcher now suffers acute short-term memory loss which leaves her unsettled at public gatherings. It’s why trips beyond her home are severely restricted. To try to fill the yawning gap left by her two children’s absence on Christmas Day, her police protection officers agreed to visit Lady Thatcher for a glass of fizz before she sat down to a traditional lunch with Kate. She then planned to watch the Queen’s Christmas broadcast.

But then, suddenly, she received a late invitation from a member of the Thatcher family. Not from either of her children, though. It was from Lady Thatcher’s niece Jane Mayes, the only daughter of her older sister Muriel, who died aged 83 after a long illness in 2004.

Muriel was the elder of the two sisters by four years.

When Jane, who is a senior employee in the personnel and development office at the Methodist Church HQ in north London, discovered only days before Christmas that her aunt was going to be alone, she immediately changed her own plans.

Lady Thatcher and her carer Kate were invited to join Jane, her husband, and her father on Christmas Day at their family home in north-east London.

“It was a late invitation and a very welcome one,” says a friend of Lady Thatcher. “Kate accompanied her and they had a lovely day. It was very quiet. Very peaceful.

“But very special.”

- Andrew Pierce