The Queen has been saddened by the death of former prime minister Baroness Thatcher, Buckingham Palace said.
The Queen will send her family a private message of sympathy after the Baroness died peacefully on Monday morning following a stroke. Buckingham Palace said in a statement: "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."
Work and Pensions Secretary Iain Duncan Smith said Baroness Thatcher was "the reason I came into politics". He said: "Watching her set out to change Britain for the better in 1979 made me believe there was, at last, real purpose and real leadership in politics once again. She bestrode the political world like a colossus. This is dreadfully sad news and my thoughts and prayers are with her family."
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. She may have divided opinion during her time in politics but everyone will be united today in acknowledging the strength of her personality and the radicalism of her politics. My thoughts are with her family and friends."
Labour leader Ed Miliband said: "I send my deep condolences to Lady Thatcher's family, in particular Mark and Carol Thatcher. She will be remembered as a unique figure. She reshaped the politics of a whole generation. She was Britain's first woman Prime Minister. She moved the centre ground of British politics and was a huge figure on the world stage.
Sir John Major, who took over as PM from Mrs Thatcher in 1990, said that while she had been keen on the poll tax, many in the Conservative Party had been against it and this had led to serious policy discussions.
He told Sky News he had enjoyed a good relationship with Mrs Thatcher when he was in her cabinet, and that this relationship had remained good for a time after he became premier.
Archbishop of Canterbury Justin Welby said: "It was with sadness that I heard the news of the death of Baroness Thatcher and my prayers are with her son and daughter, her grandchildren, family and friends.
"It is right that today we give thanks for a life devoted to public service, acknowledging also the faith that inspired and sustained her."
Home Secretary Theresa May said: "I was very sad to hear of Baroness Thatcher's death, and my thoughts are with her family at this time. Margaret Thatcher was one of the giants of the 20th century and one of our greatest prime ministers."