If a TV soap actor vacates a role, the character is wont to return with a new head on and no questions asked. When Heath Ledger died in the saddle, Hollywood drafted in a triptych of actors to complete the movie. But the sudden demise of Ian Richardson, 18 months after his first radio performance for 20 years, seemed to have spelled an end to the waspish comedy series, The Pickerskill Detentions, which I hailed in 2005 as "glorious".

Certainly, plans by independent producer Curtains for Radio to take it to television were ditched, presumably because only Richardson offered that elusive combination of bankability and credibility. Andrew McGibbon's creation, dark, satiric and with a hint of classical nemesis in every sting in the tail story, was too good to be lost to radio and it has returned in a new series as The Pickerskill Reports, undiminished by time and tragedy.

Ian McDiarmid has stepped brilliantly into the central role of the former schoolmaster, commenting from near and far on the malign activities of his former students, witticisms dispensed with vinegary glee, his plummy satisfaction as he outwits them conveyed with a baleful undertone. Each episode is an account of a different pupil who is outstanding for all the wrong reasons. However slippery the little devils are, they cannot outsmart Pickerskill, who has the forensic abilities of a murder squad veteran and the psychometric testing skills of an occupational psychiatrist.

His first subject is, in Pickerskill's estimation, a sociopath. He soon stumbles on Walter Hindle-Rand's plot to bribe the alcoholic maths master, dubbed the "meths master", with altar wine, in exchange for academic favours. Thomas Sangster played the boy in a performance in which the angelic facade of the choir boy was peeled away to reveal youthful cruelty in action. McGibbon's evocation of a boys' school in the sixties was like The History Boys stripped bare of idealism, a jungly training ground for the world. This was laugh out loud comedy, stabs of truth doled out with the humour.

Ian McDiarmid plays Dr Henry Pickerskill, retired teacher of English at a now defunct boys' public school. What he's always looked out for are oddities, the boys who didn't conform to the solid stereotype, the spirited iconoclasts, prizing them for their originality. That means, of course, the ones with a bent for junior criminality. This is his series of reports on such chaps, what happened at the school and later. It's very funny, in a sinister, sarcastic sort of way, beautifully written (by Andrew McGibbon), and brilliantly played.

Phil Cornwell (Dead Ringers, Stella Street) heads the cast of this new sitcom from Andrew McGibbon. Dave Kafka is a typical Cockney geezer, returning to a London housing estate after a spell 'inside'. Felix Dexter and Tony Gardner also star. Intriguingly, this radio show will also be broadcast as a film on BBC interactive (i.e., via the red button). How will that work, I wonder?