Former British Prime Minister Margaret Thatcher, the "Iron Lady" who dominated British politics for more than a decade, was admitted to hospital yesterday after complaining of feeling faint.

Ms Thatcher, 80, who held office from 1979 to 1990 as Britain's first female prime minister, will stay in a London hospital overnight for tests, a spokeswoman for the Conservative Party said.

"She was taken into hospital this afternoon after feeling faint," the spokeswoman said. "She is having tests."

No further details would be released, she said. The BBC reported that Ms Thatcher began to feel faint on a visit to the hairdressers and was taken to hospital by her bodyguards.

A spokesman for the Chelsea and Westminster Hospital in central London said Ms Thatcher would stay in overnight.

"She has had a number of tests and she will remain in hospital overnight as a precaution," Mark Purcell said.

"She will be assessed by doctors in the morning. Her condition is stable and comfortable and she is now resting."

Her spokesman Mark Worthington could not be reached for comment.

Ms Thatcher was taken ill on the day the Conservative Party's new leader David Cameron, 39, faced Prime Minister Tony Blair in parliament for the first time.

The Conservative Party is struggling to rebuild after years in the political wilderness.

Ms Thatcher took power in a national election on May 3, 1979, and launched into a programme of social and economic reform.

The grocer's daughter became one of the West's best-known figures, famous for "hand bagging" her opponents.

In Europe, she demanded a huge refund on Britain's contributions to the budget and brought Community business to a virtual standstill until she got it.

The late French president Francois Mitterrand memorably said she had "the eyes of Caligula and the lips of Marilyn Monroe".