High Cockalorum is a League Of Gentlemen reunion in personnel, if not in tone.

Rather than sinister and surreal, this Radio 4 comedy-drama is an affectionate and charming account of a fictional encounter between James Mason and Marty, a record company plugger employed to drive him between interviews around Yorkshire to promote the soundtrack to The Water Babies.

I say ‘fictional’, but it is based on League writer Jeremy Dyson’s uncle, who really was tasked with ferrying the fading Hollywood star around on just such a tour.

The year is 1978, a time of social change that’s reflected in music  as old rockers give way to the new wave (including a nice reference to The Fabulous Poodles ‘John Peel’s favourite band’ and where comic Ronnie Golden started). Marty is an absolute pop culture nerd, always quick to share every bit of trivia, however unwanted his contribution.

He gets off on the wrong foot with Mason when he’s late for the airport pick-up, while his garrulous nature further irritates his celebrity passenger, who only wants a quiet ride. 

As Marty persists in awkwardly off-colour jokes and fan-boy questions, it eventually becomes too much for the star, and his weary tetchiness explodes into anger. That turns out to mark a thawing of their icy relationship as Mason immediately regrets his overreaction. 

Marty is delighted to be able to chat to the bona fide star of A Star Is Born, North by Northwest and Lolita – while Mason, too, finds pleasure in having a Relatively Normal conversation with a relatively  normal man, away from the phoniness. 

Mark Gatiss – who’s brilliantly evoked Mason’s contemporary Sir John Gielgud on stage – does a sterling job here in conjuring up the modest, rather shy star dismissive of showbusiness folderol. Remarkably, he plays Marty, too, though the casual listener would not realise he was talking to himself, so complete is the characterisation.

His League co-stars pop up in various supporting roles. You might detect a diluted version of Restart course leader Pauline in Reece Shearsmith’s gossipy librarian character, while Pemberton is nicely officious as a jobsworth parking attendant, among others. 

These scenes provide comic moments, while the relationship between Mason and Marty – kindred spirits whose lives turned out tremendously different – gives the show an affectionate warmth, not to mention an undercurrent of profundity as they mull what really matters. ‘It’s the privilege of a lifetime to become who you truly are,’ concludes Mason, paraphrasing American author Joseph Campbell.

Entertaining diversions also matter in life, and on that count, High Cockalorum fits the bill.

• High Cockalorum is on Radio 4 and BBC Sounds at 2.15pm