Three of the world's most eminent former leaders, Baroness Thatcher, George HW Bush, and Nelson Mandela, will be in hospital on Christmas Day.

The 87-year-old former UK prime minister is recovering after being operated on three days ago to remove a growth from her bladder after suffering pain.

Former US president Mr Bush has developed a fever and weakness following a month-long, bronchitis-like cough.

And Mr Mandela's doctors confirmed on Monday that he was not fit to leave hospital in Pretoria.

A spokeswoman for Baroness Thatcher said she was "in good spirits" but is not expected to be released from hospital for a few days.

The veteran ex-premier's public appearances have been very restricted over recent years due to continued ill health.

She was unable to join the Queen for a Diamond Jubilee lunch with former and serving prime ministers this summer and missed an 85th birthday party thrown for her at 10 Downing Street.

In October she was sufficiently well, however, to mark her 87th birthday with lunch at a restaurant in London's exclusive St James's district with her son Mark and his wife.

Her health was thrust into the global spotlight this year when Meryl Streep starred in a controversial Hollywood film, The Iron Lady, about her. The film drew criticism from Prime Minister David Cameron and others for concentrating on the dementia she has suffered after a series of small strokes.

A hospital spokesman had said the 88-year-old Mr Bush would be released in time to spend the holiday at home, but that changed he after developed a fever.

"He's had a few setbacks. Late last week, he had a few low-energy days followed by a low-grade fever," Jim McGrath, Mr Bush's spokesman, said.

"Doctors still say they are cautiously optimistic, but every time they get over one thing, another thing pops up."

He said the cough that initially brought Mr Bush to the hospital on November 23 is now evident only about once a day, and the fever appears to be under control, although doctors are still working to get the right balance in Mr Bush's medications. No discharge date has been set.

"Given his current condition, doctors just want to hang on to him," Mr McGrath said. He did not know what had caused the fever.

Mr Bush's son, George W. Bush, the 43rd president, has been among the visitors at the hospital.

Being in the hospital for such a long time has not been easy for Mr Bush, who is accustomed to being active, Mr McGrath said. But the president has said he's determined "not to get grumpy about it".

"He's just the most relentlessly positive person," Mr McGrath said, and "he does enjoy joking with the nurses".

Mr Mandela was admitted to hospital on December 8. He was diagnosed with a lung infection and had a procedure to remove gallstones. Officials have said he is improving and is responding to treatment.

South African president Jacob Zuma said the whole country is behind Mr Mandela and he urged people to keep the former president in their thoughts on Christmas Day and throughout the festive season.

Mr Zuma describes Mr Mandela, who was imprisoned under apartheid for 27 years, as an "ardent fighter".