"She is (at the hospital) at the moment and she's fine," said public relations executive Lord Tim Bell, who advised the 87-year-old "Iron Lady" for her three general election victories.

He told AFP that her daughter Carol was at her side and that he had "no idea at all" when Thatcher would leave hospital, though earlier he had said it was possible she would remain there over Christmas.

The former Conservative Party leader, Britain's prime minister from 1979 to 1990, was admitted to hospital on Thursday for what Bell had described as "minimally invasive surgery".

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

In recent years, Thatcher -- the 20th century's longest continuous occupant of 10 Downing Street and Britain's only female premier -- has cut a subdued figure.

After a series of minor strokes, she was told by doctors to quit public speaking in 2002. With dementia taking hold, she has appeared increasingly rarely in public.

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