Former Prime Minister Baroness Thatcher has died "peacefully" at the age of 87 after suffering a stroke while staying at the Ritz hotel in central London.
David Cameron called her a "great Briton" and the Queen spoke of her sadness at the death.
Lady Thatcher was Conservative prime minister from 1979 to 1990. She was the first woman to hold the role.
She will not have a state funeral but will be accorded the same status as Princess Diana and the Queen Mother.
The ceremony, with full military honours, will take place at London's St Paul's Cathedral.
The union jack above Number 10 Downing Street has been lowered to half-mast while Parliament will be recalled from its Easter recess on Wednesday to enable MPs to pay tributes to the former prime minister.
The "Iron Lady" was by no means a nice person. Her drive to place government under the aegis of private industry, smother union labor and her support of the Apartheid-era South African and Pinochet-era Chilean governments puts her in the doghouse, for all intents. Unfortunately, Brits will now have the pleasure of seeing her legacy rewritten in the same way as done for conservative America's dearly sainted Ronald Reagan.
Still, that doesn't mean anyone has the right to call her the C-word.