The daughter of former UK prime minister Margaret Thatcher has spoken for the first time about her mother's struggle with dementia.

In her new book, serialised in the Mail on Sunday, Carol Thatcher says she first noticed her mother's memory was failing over lunch in 2000.

She says she "almost fell off her chair" seeing her mother struggle.

Baroness Thatcher, 82, had to be reminded several times her husband, Sir Denis, had died, Ms Thatcher says.

In her book, A Swim-On Part in the Goldfish Bowl: A Memoir, she tells of how her mother's "blotting-paper brain", which had always absorbed information, began to fail eight years ago - a decade after leaving power.