Son of a Viennese millionaire; irascible school teacher; WWI Germany infantryman; hospital porter; naturalised Briton - it seems sometimes as though the last thing Ludwig Wittgenstein wanted to be known for was the philosophy that made him. Produced by one-time political agitator Tariq Ali, co-scripted by Marxist professor Terry Eagleton, directed by arguably the world's most out Gay director Derek Jarman, Wittgenstein has all the built-in box office appeal of those utterly avoidable late night Channel 4 documentaries on Important Things. And it was indeed Channel 4 who stumped up the two hundred thousand pounds it took to make (hardly a large TV budget, and minuscule in cinema terms), but what they get in return is a tight, witty, engaging gem of a feature.

Jarman rejects the standard costume drama conventions, opting for an all encompassing jet black background into and against which his performers move, flawlessly lit. There are no sets to speak of, just occasional props - thus a post-box is England, a piano Vienna, and so forth. Working with limited resources, the money is sensibly ploughed into the actors and costumes to carry the piece, and with such a low-key but accomplished cast the results are seamless. John Quentin is the passive, stick-like Maynard Keynes in a succession of delightful pastel shades; the redoubtable Michael Gough the fatherly, reproving grand old man of British philosophy, Bertrand Russell; and regular Jarman muse Tilda Swinton is a joy as the decadent Ottoline Morrell in a steady stream of ever more outrageous, primary-coloured feather-gowns.

Wittgenstein himself is played by Karl Johnson and Clancy Chassy as man and boy respectively, the latter a boastful, charmingly precocious, self-confessed prodigy. It falls to Johnson to flesh the piece and provide much of the emotional depth that ultimately gives the film its undoubted resonance. His is a portrait of a man wracked by the doubt of his own work and the belief in the dignity of labour over his mere philosophising, and is a concentrated, riven, hugely sympathetic showing, especially in the understated death from cancer in 1953.

The real strength of Jarman's film however is in its ability to tackle the humanity of its subject against the essential truth of Wittgenstein's work, but without ever sacrificing one for the other. Thus ideas and argument are slipped into conversation or presented in a blackboard primer, becoming one with the narrative flow, never jarring or hectoring. The ability of the film to master the addition of a green Martian ("You can call me Mr. Green") into a discussion on the nature of reality is testimony equally to Jarman's playfulness and his adroit open-ended handling to encompass metaphor and invention to startling effect; this is a film of high-learning that never talks down to its audience.

Even for a director of Jarman's low budget alchemy, Wittgenstein is a minimalist piece, but as with his biopic of Carravaggio or his wonderful recent reading of Marlowe's Edward II, lack of money breeds in him an ingenuity and humour that speaks volumes more than many films made on twenty or thirty times the budget. This is a bright, sagacious, essentially humane film portrait of a remarkable man, by a remarkable man. A joy from start to finish.