Britain's former prime minister Margaret Thatcher was in hospital for a fifth day on Monday as she recovers from bladder surgery, a spokeswoman said.

There was no change in Thatcher's condition from Sunday when the 87-year-old was said to be "in good spirits", the spokeswoman added.

The former premier was admitted to hospital on Thursday for a minor operation to remove a growth in her bladder after suffering pain earlier in the week, and is expected to remain in hospital over Christmas.

The former Conservative Party leader was Britain's prime minister from 1979 to 1990 and remains the only woman premier in British history.

Public relations executive Tim Bell, who advised the "Iron Lady" for her three general election victories, said Sunday that Thatcher was doing "fine" after an operation he described as "minimally invasive surgery".

"She is (at the hospital) at the moment and she's fine," he told AFP.

He added that Thatcher's daughter Carol was at her side and that he had "no idea at all" when the former premier would leave hospital.

On Friday, the office of current Conservative Prime Minister David Cameron wrote on Twitter that the "PM wishes Lady Thatcher a speedy recovery".

Thatcher -- the 20th century's longest continuous occupant of 10 Downing Street -- suffers from dementia and has appeared increasingly rarely in public in recent years.

Her daughter once revealed that the former premier had to be repeatedly reminded that her husband Denis had died in 2003.

She was told by doctors to quit public speaking in 2002 after a series of minor strokes.

[Image via Agence France-Presse]