With the Union Jack at half-staff over No. 10 Downing Street, Britain on Monday embarked on a period of mourning for its most transformative peacetime prime minister, Margaret Thatcher, whose death after a long battle with dementia provoked a wave of emotive reflection from a normally stoic nation still deeply divided by her legacy.

Britain prepared for the most elaborate send-off of any
prime minister since Winston Churchill. Thatcher, who was 87, will not have a state funeral — a rare event typically reserved for monarchs here. But in a nod to the late prime minister as a molder of history both inside and outside Britain, Queen Elizabeth II consented to honor her with a final farewell — including military honors, a parade through central London and a service at St. Paul’s Cathedral next week — of the same ceremonial status as the 1997 national goodbye to Diana, Princess of Wales.

In the meantime, her passing has Britain once again coming face to face with the legacy of a woman who reshaped Britain and whose fingerprints still mark the most heated issues — from welfare reform to London’s membership in the European Union — confronting this nation today.

In death as in life, no figure seems to polarize Britain more. Ned Donovan, a 19-year-old university student and resident of the upscale Chelsea neighborhood, went by Thatcher’s cream-colored Georgian townhouse in London’s Chester Square on Monday to place a massive bouquet of lilies, joining a stream of people leaving notes and mementos outside her home. “I wasn’t alive for her premiership, but . . . if it weren’t for her, Britain would be a very different place today. I thought I should do my best to honor her.”

Yet, a few moments later, Mez Tyson-Brown, 23, a London electrician, plunked a pint of milk at her doorstep in what he called a statement against her assault on social welfare in the 1970s and 1980s — including her bid to eliminate free milk in schools — which forever changed the lives of the British underclasses.

“As a child, she took my milk away,” he said. “I’m not a big fan of hers. She tore apart the unions. She messed up social housing. She basically tore apart this country.”

As her health declined in recent years, Thatcher largely faded from public life. Occasionally she was spotted walking, with aid, up the stairs of the Ritz Hotel — to calls from bystanders with smartphone cameras of “Maggie, Maggie! This way!” Thatcher suffered her fatal stroke at the Ritz, the London landmark and her long-
beloved haunt. A hotel employee said she had been staying in a room there under the watchful eye of her caregivers.

And yet, such was her larger- than-life image that Thatcher was never far from the political debate. A recent release of documents from the Falklands War era underscored the steely determination — she was called “The Iron Lady” — she showed in defending Britain’s interests. On Monday, the political right particularly mourned the loss of its matriarch, a woman who reinvigorated a nation that, when she came to power, had entered a period of accelerated decline.

In 1990, Thatcher was forced out of office by a rebellion within her own Conservative Party. On Monday, John Major, the Conservative who succeeded her as prime minister, said the party remained damaged for years by what he called a political “matricide.” He told the BBC that following in Thatcher’s footsteps was tough. “She made the wind, instead of being bent by it.”

Prime Minister David Cameron, who won the premiership back for the Conservatives in 2010, said, “It is over 30 years since she stood here in Downing Street for the first time, and her impact here and abroad is still remarkable. When you negotiate in Brussels, it is still her rebate you are defending. When you stand in Budapest, Warsaw or Prague, you are standing in nations whose liberty she always stood up for.” And, he continued, “when people said that Britain could not be great again, she proved them wrong.”

Speaking to reporters in London on Monday, liberal firebrand Ken Livingstone, the former mayor of London, fiercely contradicted that image. “The trouble is that almost everything that’s wrong with Britain today is her legacy,” he said. “She created today’s housing crisis, she created today’s banking crisis, and she created the benefits crisis.”

Yet most of her critics, who consider Thatcher the bane of the common man and a leader who was bent on destroying the welfare state, acknowledged the passing of a truly formidable woman.

“She reshaped the politics of a whole generation,” said Ed Miliband, head of the Labor Party, Thatcher’s longtime nemesis. “The Labor 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.”

Eliza Mackintosh contributed to this report.