Thatcher: My mother's dementia battle

In her new book, Carol Thatcher said she first noticed her mother's failing memory while the pair had lunch in 2000.

She also disclosed that she had to repeatedly break the "truly awful" news of her father Sir Denis' death to her mother until the information sank in.

In her book, A Swim-On Part in the Goldfish Bowl: A Memoir, she wrote how her 82-year-old mother's "blotting-paper brain" which had always absorbed information got confused between Bosnia and the Falklands during a conversation about the war in the former Yugoslavia.

She wrote: "I almost fell off my chair. Watching her struggle with her words and her memory, I couldn't believe it. She was in her 75th year but I had always thought of her as ageless, timeless and 100% cast-iron damage-proof.

"The contrast was all the more striking because, until that point, she'd always had a memory like a website."

In the book, serialised in the Mail on Sunday, Ms Thatcher added: "From the fateful day of our lunch, telltale signs that something wasn't quite right began to emerge.

"Whereas previously you would never have had to say anything to her twice, because she'd already filed it away in her formidable memory bank, 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.

Recalling Sir Denis' death from pancreatic cancer in 2003, she said: "Losing Dad ... was truly awful for Mum, not least because her dementia meant she kept forgetting he was dead."