Last surviving child of Winston Churchill

Mary Soames, who has died aged 91, was the last surviving child of Britain's wartime prime minister, Winston Churchill.

She spent an idyllic childhood at Chartwell, the family estate in Kent, where she tamed fox cubs, raised orphan lambs and played in a brick house built for her by her father – whose hobbies included bricklaying.

Guests at Chartwell included Charlie Chaplin, who amused her by impersonating Napoleon, and TE Lawrence, better known as Lawrence of Arabia, who dressed up in his Arab robes. On the eve of the second World War Noel Coward sang Mad Dogs and Englishmen to her family and their guests.

During the war, after overhearing a general advising her father that England should seek women for understaffed anti-aircraft batteries she enlisted as a private without his knowledge.

She accompanied Churchill to summit meetings as his personal aide, including the Potsdam conference in 1945, where her father, President Harry S Truman and Soviet leader Josef Stalin planned the postwar world. She found Stalin "small, dapper and rather twinkly".

After several ill-fated romances she married Christopher Soames, a dashing member of the Coldstream Guards, and nurtured his career as Tory politician, ambassador to France and last governor of Southern Rhodesia (now Zimbabwe). They had five children.

National Theatre She became Lady Soames when Christopher was knighted in 1972. After her husband’s death in 1987, she chaired the National Theatre for six years. But her most notable personal achievement was a series of books she wrote about her family.

The first, Clementine Churchill: The Biography of a Marriage (1979), a biography of her mother, won the Wolfson History Prize. Soames described her mother as "an old-fashioned radical" with "latent hostility toward the Tory Party", which her husband happened to lead.

Her other books included an annotated family photo album, a study of Churchill as a painter and a 702-page collection of letters between the prime minister and his wife.

Soames later came to be regarded as something of a national treasure. She was named a fellow of the Royal Society of Literature and a Dame of the British Empire. In 2005, Queen Elizabeth appointed her a Ladies Companion of the Garter, Britain’s highest chivalric order.

After the death of former prime minister Margaret Thatcher in 2013, she was one of only two living nonroyal women to be so honoured. The other is Eliza Manningham-Buller, who commanded Britain's counterterrorism efforts as head of MI5, the internal security agency, from 2002 to 2007.

Mary Spencer-Churchill was born at Chartwell in 1922. A year earlier, her sister Marigold had died, aged 2½, of tonsillitis. Her arrival, she wrote, helped compensate her parents for their loss; she was, she said, “a child of consolation”.

Her living siblings were so much older – Diana by 13 years, Randolph by 11 and Sarah by eight – that she regarded them as “godlike Olympian figures”. As a girl, she lived almost entirely with grown-ups. Her father wrote that at five, she spoke “in the tone and style of a woman of 30”. A rock of stability He doted on her, but she said she did not become close to her mother until her adolescence. During her early youth, her closest companion was her nanny, Maryott Whyte, a first cousin of her mother and a trained nurse.

Soames once attributed the divorces, substance abuse and relatively early deaths of her siblings to their lack of a rock of stability like Whyte. “I don’t know why I turned out like this while the others had such problems,” she said in a 2002 interview, “and comparisons are always odious, aren’t they? But I do think Nana made a great difference.”

During the war, Soames was briefly engaged to the son of an earl and also had a romance with an American army officer. In 1946, she and her father made a private trip to Belgium with the apparent goal of her becoming engaged to Prince Charles, who was ruling the country as regent. On September 27th, the press reported that an engagement announcement was likely the next day. That never happened.

Being Christopher Soames’s wife involved staging famously entertaining parties in Paris. It also meant speaking off the cuff to 900 guerrillas in Rhodesia.

Soames, short and stocky like her father and perhaps as stubborn, savoured a fine cigar. After she quit smoking, she auctioned off the family stash of Havanas for more than £130.000.

She is survived by her children, Nicholas, Emma, Charlotte, Jeremy and Rupert, and a number of grandchildren and great-grandchildren