The book, "A Swim-On Part in the Goldfish Bowl: A Memoir" is being serialised in the Mail on Sunday.

In it Carol Thatcher says that she first noticed her mother's memory was failing in 2000 at a lunch meeting.
When her mother muddled up the Falklands war with the Bosnian conflict.
She says she "almost fell off her chair" seeing her mother struggle.

Baroness Thatcher, 82, had to be reminded of her husband's death over and over again. 'Every time it finally sank in she'd look at me sadly and say "Oh" as I struggled to compose myself,' Thatcher writes. '"Were we all there?" she'd ask sadly.'

Ms Thatcher says "Mum started asking the same questions over and over again, unaware she was doing so. "It might be something innocuous - such as 'What time is my car coming?' or 'When am I going to the hairdresser?' - but the fact she needed to repeat them opened a new and frightening chapter in our lives."

Background

Margaret Hilda Thatcher, Baroness Thatcher LG, OM, PC, FRS (née Roberts); born 13 October 1925(1925-10-13) is a British politician, who was Prime Minister of the United Kingdom from 1979 to 1990 and Leader of the Conservative Party from 1975 to 1990. She is the first and only woman to date to hold either post.

Born in Grantham in Lincolnshire, England, she went on to read Chemistry at Somerville College, Oxford. She was selected as Conservative candidate for Finchley in 1958 and won the seat in the general election the following year. Upon the election of Edward Heath in 1970, Thatcher was appointed Secretary of State for Education and Science. In 1974, she backed Sir Keith Joseph for the Conservative party leader, but after falling short he dropped out of the race. Thatcher entered herself and became leader of the Conservative party in 1975. As the Conservative party maintained leads in most polls, Thatcher went on to become Britain's Prime Minister in the 1979 General Election.

Thatcher's tenure as Prime Minister was the longest since that of Lord Salisbury and was the longest continuous period in office since the tenure of Lord Liverpool who was Prime Minister in the early 19th century. She was the first woman to lead a major political party in the UK, and the first of only three women to have held any of the four great offices of state. Among other things, she defiantly opposed the Soviet Union, and her tough-talking rhetoric gained her the nickname the "Iron Lady".

She currently has a life peerage as Baroness Thatcher, of Kesteven in the County of Lincolnshire, which entitles her to sit in the House of Lords.