Why mystery man Marlow's return is music to the ears

It was actor Patrick Malahide's naked bottom among the forest bracken that really excited the tabloids in late 1986 – thus beginning the denigration of Britain's greatest television dramatist, Dennis Potter, into the handy red-top label of "Dirty Den". More sophisticated viewers of Potter's The Singing Detective admired the enigmatic sauciness in Joanne Whalley's eyes, as her Nurse Mills rubbed cream on the nether regions of bed-prone author Philip E Marlow (played by Michael Gambon). Either way, the frank sexual scenes were only one part of Potter's masterpiece, and should not distract today's more mature TV audience.

For tomorrow night The Singing Detective earns a belated 25th anniversary screening on BBC4. The BBC had wanted to screen it on its actual birthday last November, but was £5,000 short of the repeat fees requested by the Potter estate. Labour peer Lord Hollick made a direct approach to BBC director-general, Mark Thompson, offering to make up the shortfall, but Thompson suggested such a personal donation might be unethical. In the end, some sort of deal seems to have been struck with the Potter estate, and it is licence money well spent. I can also see why the altruistic Hollick might have thought it five grand gainfully parted with – a gift to the nation, in fact.

The Singing Detective is the supreme distillation of Potter's themes and dramatic style, especially the sudden switching into musical numbers in which the actors lip-synched to old songs. It was a technique he first used in Pennies from Heaven in 1978 (using the pop songs of the 1930s), and would use again in the final part of this loose – and loosely autobiographical – trilogy, the lesser but still underrated Lipstick on Your Collar (made for Channel 4 in 1993). Potter once famously remarked on "the strange potency of cheap music", and perhaps it was the juxtaposition of "The Teddy Bear's Picnic" with Malahide's buttocks that so roused Fleet Street.

The story involves blocked thriller writer Philip E Marlow (Gambon in the role that rightly made his name), who is hospitalised due to the acute skin and joint condition – the same psoriatic arthritis from which Potter suffered. "Even tears hurt the bloody skin on my face," says Marlow at one point, just before his consultant, and attendant doctors and nurses, break to a bravura production of "Dem Bones". Refusing medication and jousting with a psychoanalyst played by Bill Paterson ("so psychoanalysis isn't nasty enough for you... now you want to get into literary criticism"), Marlow drifts into the world of his uncompleted novel, the Chandleresque The Singing Detective, and memories of his childhood in the Forest of Dean. "It's a detective story about how you find yourself," Potter said.

Like a lot of his work, it is simultaneously deeply sophisticated and wonderfully accessible, more accessible perhaps than the academic view of The Singing Detective (as posited on its website by the Museum of Broadcast Communications in Chicago) – that it was "British television's most sustained experiment with classic post-Brechtian strategies for anti-realism, reflexivity, textual deconstruction, and for the encouragement of new reading practices on the part of the TV spectator". Quite so, but such analysis doesn't begin to hint at joys of The Singing Detective – its sheer wit and verve, profundity and poignancy. British television hasn't seen its like since, and perhaps never will again.

Like Pennies from Heaven, it was remade as a Hollywood film, this one starring Robert Downey Jr. But don't miss this chance to see the real thing – for unlike many classics from television's "golden age", which can seem slow and dated now, it truly stands the test of time.

'The Singing Detective' starts tomorrow at 9pm on BBC4