By her own design and the good offices of those who care for her, we neither see nor hear the grocer’s daughter from Grantham whose name alone inspires litanies of loathing or ecstatic eulogies in any Briton over the age of 30.

It is right and fitting that Lady Thatcher, at 82, is living a sequestered life. It has been generally understood, though scarcely mentioned, that her mental acuity, once formidable, isn’t what it was. It was deemed appropriate to maintain her considerable dignity, foster her legacy and preserve her peaceful existence in a quiet, discreet, behind-closed-doors manner.

Until now that is. Her daughter Carol, Queen of the I’m A Celebrity… jungle, has seen fit to puncture her own
mother’s privacy. For the sake of a book, tellingly entitled A Swim-On Part In The Goldfish Bowl, journalist Carol has unleashed an unwelcome torrent of details about her mother’s dementia.

We are told, for example, a fact long considered too achingly poignant to be discussed even in Fleet Street circles. Carol reveals that her mother forgets her beloved husband Denis is dead. Each day brings fresh agony as Denis Thatcher’s widow must be reminded, yet again, of her agonising loss.

Carol peppers the book with scenes of her mother’s dementia. Sometimes Lady Thatcher can “hardly remember the beginning of a sentence by the time she gets to the end”. Sometimes she forgets a newspaper headline she has only just read. Sometimes she “struggles with words and can’t recall what she had for breakfast”.

Such disclosures would be fine and fair from any concerned daughter writing about any mother. The issue here is that Lady Thatcher is not just any mother.

Those of us who heard her “We are a grandmother” speech are in absolutely no doubt of that. Baroness Thatcher is not merely herself. She is far more than the sum of her parts.

She still resides in all that she achieved, all those she aggrieved, all she meant to this country and the indelible mark she left on the rest of the world. To reduce this gigantic figure to an ailing geriatric who forgets whether she had porridge or prunes is an unworthy, even unkind act.

Lady Thatcher deserves more than to have her dementia paraded and picked over while she is still alive to feel – in her lucid moments – the embarrassment.

We deserve more, too. Whatever her motive in contributing to the dismantling of this august image, Carol Thatcher, who admits to a chequered relationship with her mother, should question it.

Let icons be icons. The only appropriate publication date for a book like this should be many years after Lady Thatcher’s State funeral.