I begin with a chuckle that turns into a lament. The Pickerskill Reports, the series in which a former public school master reminisces in a tone as lacerating as it is fond, is no more. Author and director Andrew McGibbon has declared it's a wrap with The Last Report, bringing bank-holiday merriment with its mix of the scholarly and the fantastical in a one-off special.

The series originally starred Ian Richardson, whose recruitment was a coup in itself and whose performance so matched the withering put-downs and acute insights of the script that all seemed lost for the show after his death in 2007.

Yet producer Curtains For Radio brought the series back in 2009 with another casting triumph - with his reedy-voiced enunciation and donnish demeanour, Ian McDiarmid stepped effortlessly into the other Ian's footsteps. This new play finds McDiarmid in full flight, relishing the effortless dialogue ("brandishing your braggadocio"), high-table erudition and gentle, literate comedy that can turn savage in a second.

As the 'progressive' head, Michael Feast fuses the sinister and the cynical, while Tony Gardner is the spluttering maths master Lefty, around whom Thomas Brodie-Sangster's precocious pupil, Porter, runs rings. With her girlish politeness, Elaine Cassidy is the antithesis of a villainess - until she is revealed to be working for the kind of suspect organisation beloved of 1960's TV series such as The Avengers.

Before Richardson's death, there was dangerous talk of a transfer to television, but perhaps The Pickerskill Reports is best remembered as one of radio's timeless jewels.

Very last episode of the witty social satire, blessed by a superb cast (Ian McDiarmid, Mark Heap and Michael Feast), written and directed by Andrew McGibbon. McDiarmid plays the wily head of a school which has gone through many transformations and whose past pupils duly represent the fact, whether pillars of the establishment, captains of industry or various other grades of dodgy geezer. Now meet Faye (Elaine Cassidy) who will save its site from mercantile exploitation to transform it into a beacon of the new educational ethos.

This long-running black comedy starring Ian McDiarmid as Dr Pickerskill, a retired English master looking back at the lives of his most entertaining pupils at Haunchurst School, draws to a close with a special send-off. In The Final Report, written by Andrew McGibbon, Pickerskill has to contend with a charismatic cult leader called Faye, whose shady sect, The Constancy, is planning to take over the college. Elaine Cassidy and Mark Heap also star.

I Think I've Got a Problem is a gem from the comedy archive, featuring the late Bob Monkhouse as a psychiatrist and Suggs (lead singer from Madness) as Tom, his patient, who wakes up one day to find he can't stop singing. By Nick Romero and Andrew McGibbon, it's witty, original and curiously wise.

David Nobbs, wonderfully comic writer whether on radio, TV or in print, begins a three-part series talking to an audience about his work and some people he's worked with over the years. As he's written for Frankie Howerd, David Frost and The Two Ronnies, invented such TV comedies as A Bit of a Do, The Fall and Rise of Reginald Perrin and (for Radio 4) The Maltby Collection, it's a rich field. Mia Soteriou and Martin Trenaman are the readers, Andrew McGibbon produces for independents Curtains for Radio.

Ian McDiarmid plays Dr Henry Pickerskill, a teacher at Haunchurst College for Boys in the days when it had boarders, icily remembering former pupils. Today, Patrick Trumball (Toby Longworth) who was fascinated by thunderstorms and lightning. What Dr Pickerskill spotted was that Trumball, an unusual child, also possessed a photographic memory which came in handy when the school's dodgy accountant blamed Pickerskill for a fraudulent tax return. Written and produced by Andrew McGibbon, this (all too short) series restores cynicism's good name.

The return of The Pickerskill Reports: Series 2

For four days in April an ordinary house in London became Haunchurst College for Boys, the setting for The Pickerskill Reports. The kitchen became the dining room; the garden became the college grounds, the forest, and playing fields; the living rooms the offices, staff room and study and a vaulted room, the school classroom and school hall.

He's part Betjeman, part Meldrew and part stand-up comic gunning for his audience. There can't be many Dr Henry Pickerskills alive and working now in the education system because his brand of tough love, rough justice and abrasive shafts of wit directed at his pupils would probably breach the Human Rights Act.

The Pickerskill Reports is back with more of Dr P's ironic stories of life long ago at a boys' boarding school whose ethos is one in which normal laws don't apply, let alone what would then have been fanciful libertarianism. Dr P arrives in his classroom like Dirty Harry. Nemesis of bullies, alleviator of the torment of those he calls his "spirited iconoclasts" and a complete enigma to his headmaster who, somewhere in the recesses of his brain, knows that his English teacher is running rings around him.

The head is portrayed as militaristic but feeble-minded by Mike Sarne, the actor and director who has covered much ground since he tried to persuade Wendy Richard to Come Outside in the 1962 pop song. Making a guest appearance in the first episode was Sheridan Smith, also showing her versatility as an aristocrat playing at gender politics. Ian McDiarmid, as Dr P, brings a dryness of delivery and impeccable timing to the role while clearly relishing Andrew McGibbon's sardonic and entertaining script.

Andrew McGibbon's fantastic (in every sense) comedy The Cornwell Estate had the ridiculously versatile Phil Cornwell in completely Euro-bonkers mode as Hank Zuttermilk, the Dutch lorry driver - his English an explosion of suffixed 'ishes' - his wardrobe an implosion of seventies weekend hippy gear. What makes this series work so well is the preposterousness allied with minute observation in both the writing and performance.

The welcome new series of Andrew McGibbon's The Cornwell Estate had its star, in episode two, playing a Newcastle comic banned by matrimonial injunction from entering the city centre. Instead, he devised a high altitude messaging system by attaching one of his publicity posters to a homing pigeon to semaphore reparation to the teenage daughter he had never met.

The series' co-creator Phil Cornwell plays a different character in each episode, the style of which is pitched midway between Alan Bennett and Alan Partridge. Coincidentally, the breathtakingly talented Cornwell once played a DJ in I'm Alan Partridge. This is comedy drama which holds its nerve, not always going for the obvious joke, bundling nerdiness up with edginess. The opener had Cornwell as a teacher muddling his way blindly through a minefield of potential racism as he tries to coax ethnicity from pupils whose origins may have been far-flung but who were firmly rooted in Potter's Bar.