Transfers from television to radio rarely work: they tend to be dramas and you can see and hear the original star in your head while trying to concentrate on someone else’s voice: an uneasy disconnect. Rumpole of the Bailey could only ever be Leo McKern, who played him for 14 years on ITV, and Maurice Denham became a pale imitation on radio. Dixon of Dock Green was always Jack Warner, who played him for 21 years on BBC screens, so it was never the same when David Calder took over on Radio 4. And Paul McGann was an unsatisfactory Doctor Who on BBC7, even though he had played the Time Lord once before.

Most of the traffic going the other way has been more successful. Hitchhiker’s Guide, Little Britain, Room 101, Absolute Power, Goodness Gracious Me, The League of Gentlemen, Sean Lock’s 15 Storeys High and Steve Coogan’s Knowing Me, Knowing You with Alan Partridge are just some of the shows that have switched from radio to television. But they are, in the main, comedies — and depend as much on wit, imagery, flights of fancy or clever formats as on the charisma of specific performers.

Yesterday, on Radio 4, the problem was overcome by the simple expedient of using the same star. Ian McKellen revived the role of Walter Williams, a mentally impaired man institutionalised after the death of his mother, who he played on the opening night of Channel 4 in 1982. That original, bleak and distressing play was called simply Walter. Its sequel, Walter and June, was seen in 1983. The writer, David Cook, yesterday came up with a second, warmer, sequel, Walter Now, bringing the story up to date.

The hospital where Walter spent so much of his life, whose corridors “smelt of boiled cabbage and urine”, has been closed, and turned into a business and leisure centre.

Now a pensioner, Walter has been decanted into the community. After sleeping rough, he is placed in a household with three other people: Mary, Bernard and Terry. They all have (similarly mild) learning difficulties. Mary gets pregnant: should she be allowed to have her baby? Walter is framed for indecent assault on a boy by a neighbour not keen on this quartet of mentally disabled people in the street.

It was straightforward, likeable, gripping and clearly has the legs to run further: many other listeners will have been drawn in and want to know whether Mary has her child. It was also sentimental, avoided the toughest questions and, most problematic of all, did not explain how Walter’s character had changed so much. In 1982, he was clearly handicapped, not realising that his mother’s decomposing corpse indicated that she was dead, not understanding what death meant. Now, he is wise, ironic, coherent, quietly reasonable in all he says and does and, though somewhat simple — always an attractive quality, in truth — is not disabled in any obvious sense. He is given over to neat utterances: “Knowledge is power”, he says at one point, and “Collars defeat me” when assessing his ability to iron shirts. Tellingly, he knows that his nickname is “Witless Walter”.

McKellen played him with compassion and infinite gentleness. If you believed in anything while listening to Walter Now, it was because of him. He is the greatest actor we have, 70 this year, incomparable with either prose or poetry. I wish, as I am sure many others wish, that he would appear on radio more often.

paul.donovan@sunday-times.co.uk

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