Friends and foes alike were marking the end of an era tonight after Baroness Thatcher died at the age of 87.
The ex-prime minister is to have a funeral at St Paul's Cathedral with full military honours - the same status as accorded to the Queen Mother - in recognition of her huge influence on the country.
The Queen was said to be "sad" at news of the death, while David Cameron praised her as a "great leader" and a "great Briton". For Labour, Ed Miliband said she had "moved the centre ground of British politics", and Tony Blair credited her with changing the world.
Global leaders added their voices to the tributes, with Barack Obama saying Lady Thatcher had been a "true friend" to the US.
However, others on the Left condemned the social impacts of her policies encouraging the free market and stripping power from unions. Respect MP George Galloway sparked anger by tweeting "Tramp the dirt down" - a reference to an anti-Thatcher Elvis Costello song from the 1980s.
Lady Thatcher's place in the history books was secure as soon as she won the keys to Downing Street in 1979, becoming the UK's first woman premier.
But over the next 11 years she demonstrated that she had far more to offer than her gender.
The Tory leader's impact was underlined by the reaction to her death at the Ritz Hotel in London this morning, where she suffered a stroke while recuperating following a minor operation.
Mr Cameron cut short an official trip to Europe and announced that Parliament was being recalled from its Easter recess on Wednesday to give MPs the chance to pay tribute.
Labour and the Tories have suspended campaigning ahead of next month's key local elections, and the Lib Dems are also not expecting to hold any events. Flags were flying at half-mast on public buildings.
As Lady Thatcher's health deteriorated, the issue of whether she should be granted a state funeral - as Churchill was - grew increasingly controversial.
However, it has emerged that she rejected the idea herself, and also insisted she did not want her body to lie in state or money to be spent on a fly-past.
Instead, the streets will be cleared for a procession from Westminster to St Paul's, where there will be a televised service attended by dignitaries from around the world. The event will take place next week, but the day has yet to be confirmed.
In a statement outside Number 10 this evening, Mr Cameron said: "Today we lost a great leader, a great prime minister and a great Briton.
"Margaret Thatcher didn't just lead our country - she saved our country."
Mr Cameron said Lady Thatcher had defied those who said a woman - especially a shopkeeper's daughter - could not succeed in politics.
She had fought "big political battles" against union barons, unleashed enterprise, won the the Falklands War and helped win the Cold War, he added.
"We can't deny that Lady Thatcher divided opinion. For many of us, she was and is an inspiration. For others she was a force to be defined against.
"But if there is one thing that cuts through all of this - one thing that runs through everything she did - it was her lion-hearted love for this country.
"She was the patriot prime minister and she fought for Britain's interests every single step of the way."
Mr Miliband sent his condolences to Lady Thatcher's children, 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.
"The Labour Party disagreed with much of what she did and she will always remain a controversial figure. But we can disagree and also greatly respect her political achievements and her personal strength."
Liberal Democrat leader Nick Clegg said Lady Thatcher had been one of the "defining figures in modern British politics".
Former political opponent Lord Neil Kinnock said: "I recognise and admire the great distinction of Baroness Thatcher as the first woman to become leader of a major UK political party and prime minister."
Sir John Major, who took over in Downing Street in 1990 after she was ousted, described her as a "force of nature" and a "political phenomenon".
"In government, the UK was turned around under - and in large measure because of - her leadership," he said.
Mr Obama said: "Here in America, many of us will never forget her standing shoulder to shoulder with President Reagan, reminding the world that we are not simply carried along by the currents of history - we can shape them with moral conviction, unyielding courage and iron will."
Reformist Soviet leader Mikhail Gorbachev described the former prime minister as a "heavyweight politician".
"Margaret Thatcher was a heavyweight politician and a striking person. She will remain in our memories, and in history," he said.
Lady Thatcher suffered several small strokes in 2002, and stopped accepting public speaking engagements on medical advice.
Her increasingly frail condition when she was seen - especially after the death of husband, Denis, in 2003 - led to frequent bouts of speculation about her health.
However, MPs and friends who saw her regularly said she remained alert and interested in politics until relatively recently. She was said to have been delighted that Mr Cameron, and before him, Gordon Brown extended invitations to visit 10 Downing Street and Chequers.
The Thatcher family have asked well-wishers to donate to the Royal Hospital Chelsea instead of leaving flowers.
But someone had placed a single yellow daffodil at the feet of Thatcher's statue outside the Commons chamber today.
The House of Lords has also been recalled on Wednesday, and will sit at 2.30pm - the same time as the Commons.
The Government will put down a motion, which is expected to pay tribute to Lady Thatcher, according to the Speaker's Office. The Prime Minister is then expected to give a statement to the Commons, followed by the Leader of the Opposition.
There will then be time for backbench MPs to make their own tributes to the former prime minister.
Mr Cameron phoned French president Francois Hollande this evening to apologise for cancelling the meeting they had been due to hold in Paris this evening.
A Number 10 source said the president had conveyed his condolences, and they had agreed to reschedule the talks as soon as possible.