She and her husband, John Bayley, would come to stay with my parents in Scotland, and I remember the clatter of the typewriter as they worked in the same bedroom, and the strange spectacle as they picked their way, holding hands, into the loch.

Iris once managed to set off the burglar alarm at my grandmother’s house while on a midnight quest for smoked eel in the fridge. John accidentally locked himself in the drinks cupboard, where he made a chirruping noise until he was discovered and released.

Iris and I would play poker for chocolates. She was, as one might imagine, a very good poker player, and quite ruthless. I still have a leather card-carrying case she gave me, which once belonged to her mother.

She got me my first (short-lived) job at her own publishers, and we would meet from time to time in a small, rather bad restaurant off Baker Street to discuss absolutely everything, none of which I can now recall, except the giggling.

There was always much laughter, yet from my earliest memory she was prepared to treat a mere child — and an annoying one at that — with direct and unwavering seriousness: this was both thrilling and slightly terrifying.

But by the time Iris became ill, I had already been living abroad for many years, and I barely saw her during the last phase of the unwinnable battle with Alzheimer’s — this may explain why I found Sir Richard Eyre’s film Iris, which opens on Friday, so deeply moving.

Dame Judi Dench has captured Iris in a way that is quite uncanny. Dame Judi is Dame Iris, from her walk to her voice to her wardrobe. Indeed, had Dench not been willing or able to play the part, it is hard to see how this film could have been made.

I was less comfortable, perhaps predictably, with the young Iris, played by Kate Winslet. I never knew Iris when she was young, but the character on screen seemed too wilfully self-involved, and neither sufficiently eccentric nor funny enough to be the person I knew in later life. Jim Broadbent plays the older John with great skill, but Hugh Bonneville as the young John is even better: gentle and awkward, but wonderfully wry and sharp behind the stammer.

This is the portrait of an extraordinary love affair, and of the cruel theft of words from someone who lived by and for them. I would recommend it to anyone who has watched the creeping violence of Alzheimer’s, anyone who has read a Murdoch novel, anyone who knew her and anyone who has been in deep but complicated love — which should cover just about anyone reading this.

I wish I had been around more when Iris was slowly departing. I happened to be in Britain on the night John first took her to the nursing home where she would die.

He came for supper afterwards at my mother’s home in Oxford and then we walked back together to the empty house in Charlbury Road. Amid the breathtaking domestic chaos there (an aspect of the Murdoch-Bayley home that long predated Iris’s illness and which the film does not, and could never, adequately convey) we discovered, and drank, the end of a bottle of whisky.

We talked of other things but his agony — so touchingly portrayed in this film and in his writings — filled the cluttered room.

I never saw Iris again; now, in a strange way, I feel I have. I am not an objective reviewer, but I loved Iris.