Underrated: A jigger of remorse, a dash of lunacy: Overdue credit where credit's due: Kevin Jackson kicks off a new series on the critically overlooked

It might seem perverse to suggest that Jeremy Brett's portrayals of Sherlock Holmes are in any way underrated: the Granada series has, after all, proved immensely popular not just in Britain but in more than 70 other countries (it's huge in Japan), and reviewers regularly commend its leading players, its high production values, strong supporting casts, atmospheric scores and so on. Moreover, only die-hard Basil Rathbone fans will resist the proposition that Brett makes a fine Detective, and Edward Hardwicke an engaging Dr Watson.

But even the most widespread acclaim can still be insufficient if it does not try to address its object, and popularity is not quite the same thing as recognition. The case of Mr Brett is a little like the case of the purloined letter in the Poe tale which was one of the influences on Conan Doyle. In Poe's yarn, a filched letter was overlooked precisely because the villain had not hidden it at all. Similarly, Mr Brett's true brilliance is overlooked not because no one says that he is splendid but because everybody does.

What Brett offers is a combination of fidelity and audacity. Everything he does can ultimately be justified by chapter and line from Conan Doyle's stories, but he has taken liberties with the myth so confidently that he has also, over the last decade, taken possession of it, and displaced the literary Holmes.

Brett's is a richly comic performance. His Holmes is composed of sudden wild stares, dreamy vacancies, hoarse exclamations, dulcet murmurs which wilt into silence. He holds his body stiffly yet languorously, like an opium-eater who has held a commission in the Guards, and his accent is patrician enough to make Sir Kenneth Clark sound like Danny Baker. Into this potent brew go a jigger of remorse, a dash of sheer lunacy and a strong whiff of camp - though the camp is held firmly in check by sincerity.

So much is surface, and it is glittering surface. A friend recalls a dull evening in Budapest, where he channel-hopped idly into an episode dubbed into Hungarian, and found himself beguiled even though he had only the dimmest idea of the plot. Beneath the amusing caricature, however, is one of the shrewdest interpretations of a popular myth ever filmed.

What other actors have represented in Holmes is the superbrain, the overgrown swot. What Mr Brett has given us for our own fin de siecle is a portrait of the Detective as a crazed aesthete. Conan Doyle did not only borrow the format of the detective story from Poe: he also took on board all the trappings of Poe's doomed artist-heroes, which is why Holmes is a drug addict, why he plays and composes wild music on his Stradivarius, why he dreads ennui and oscillates between lassitude and frenzy . . . and indeed, why he often quotes Poe.

Sherlock Holmes is the Roderick Usher of Baker Street, and Brett has captured him with genius. Veteran theatregoers are fond of telling their juniors that they have missed the definitive interpretations of Hamlet or Lear or Phedre. They may be right, but at least we can console ourselves that one definitive role is very much alive. The Granada series is, we can confidently assert, an ideal Holmes exhibition.