Baroness Thatcher, Britain's first female prime minister, has died at the age of 87 after suffering a stroke
The former Conservative leader won three general elections - in 1979, 1983 and 1987 - before being forced to step down in 1990. She retired fully from politics in 1992.
She had been suffering from ill health for many years including having an operation to remove a growth from her bladder in December 2012 and a series of strokes in 2002.
Prime minister David Cameron said:"Today is a truly sad day for our country. We've lost a great prime minister, a great leader, a great Briton. As our first woman prime minister, Margaret Thatcher succeeded against all the odds. And the real thing about Margaret Thatcher is she did not just lead our country, she saved our country. And I believe she will go down as the greatest British peacetime prime minister.
"Today is obviously a day we should most of all think of her family. We've lost someone great in public life, but they've lost a much-loved mother and grandmother and we should think of them today."
Liberal Democrat leader Nick Clegg said: "Margaret Thatcher was one of the defining figures in modern British politics. Whatever side of the political debate you stand on, no-one can deny that as prime minister she left a unique and lasting imprint on the country she served."
A Buckingham Palace spokesman added: "The Queen was sad to hear the news of the death of Baroness Thatcher. Her Majesty will be sending a private message of sympathy to the family."