It is a truth universally acknowledged that it can't be a proper costume drama unless it opens with a shot of a carriage rattling across the country, just so that Joe Viewer knows he's in the past and there will be tea served later. City of Vice has just about the longest opening sequence you'll ever see, as the camera travels through a sepia-tinted 3D map of 18th century London and Henry Fielding fills you in the complicated backplot of his life, in which, having abandoned his "celebrated works of fiction", he has teamed up with his half-brother John "blind since youth" to bring law and order to the lawless streets of London. As premises go, you have to admit, it's fucking awesome.

City of Vice is basically the original cop show, although in terms of atmosphere I'd say it has more in common with noir or westerns than the genteel sort of tea and cake costume drama long experience with the genre leads one to expect. There is a far degree of stretching of the facts - the Bow Street Runners were not, in fact, even remotely comparable to anything we might recognise as a police force (as far as I understand it, they were eight guys, operating exclusively out of Bow Street, whose only nod towards criminal investigation involved ganking suspects into the house for a spell of interrogation) and can only really be seen as Peel's inspiration in that the Fieldings recognised the need for a police force in the sprawling urban mess that was (and still is) London. But the idea itself - The Fielding Brothers Fight Crime! - is such a wonderful one it seems churlish to harp on about history and City of Vice is such a cunning blend of fact, fiction and speculation that it works beautifully.

It's also as British as these things come. There are about three sets and one, slightly inept cameraman although, to be fair, this adds to that authentic period feel despite my personal distaste for what is known within the industry as "poo-cam." All right, so it might not actually be called that but that's what it looks like - it debuted recently in The Libertine much to my disgust. Who wants to see Johnny Depp, as the Earl of Rochester, through a greyish-brown filter. Nobody! Anyway, returning to City of Vice: the CGI map which the viewer follows from location to location is fantastic - it lends a real sense of place and time to a concept (18th century London) which can otherwise seem rather remote and abstract. And, since I tend to watch a lot of American TV series in which all the characters, regardless of who they're supposed to be, are golden, beautiful and look about twelve years old, it's a relief to find myself back on the shores of British drama where everyone has a face like a three day old used teabag that's been left out in the rain. The two teabags in question - Iain McDiarmid and Ian Glen as Henry and John respectively - are both splendid, bringing both great ability and what seems to be genuine relish to the roles. Also I have to say, Ian Glen - perhaps because rather than in spite of the blindness - is oddly hot.

The main disappointment of the series is the fact that it is a mere five episodes long, although the final two are linked by a developing situation concerning the brothers' attempt to bring down a notorious criminal gang. Although, naturally, there's a fair degree of fabrication, especially as concerns the rudimentary investigative procedures the brothers put in place, most of the cases in which they become involved genuinely happened. And they're all pleasingly seedy, offering up an exciting cast of prostitutes, brothel madams, homosexuals, debt collectors, pimps, thieves, social climbers, villains and the Irish. There's no doubt that it's a dark and dirty world that offers little hope or justice for its inhabitants. Equally, no mistaken attempts to sanitise the brothers' morals or methods have been made: although you do root for them and respect what they are trying to do, they are quite difficult to actually like, at least from this end of the 21st century. They evince a peculiar mixture of idealism and pragmatism, idealism because they genuinely believe that a police force is necessary, cannot be in any way corrupt and that justice must be served, pragmatism because they're willing to do whatever it takes to get it, to protect each other and can admit no moral grey areas whatsoever. For example, in the third episode they become involved in the murder of a homosexual clergyman. Throughout the episode they regard the mollies as little more than criminals themselves, viewing them with an authentically eighteenth century combination of bewilderment and disgust that is actually quite difficult for the viewer to witness.

John, as Henry reminds us, was raised by a Catholic mother: consequently he's prudish and self-righteous but he has no hesitation in literally torturing another human being in order to obtain information that will help him save his brother. Henry, similarly, has utterly no concept of how extreme depths of poverty and desperation can lead people to commit criminal acts - he pays lip service to sympathy but actually, having led a somewhat sheltered life, cannot emphasise in the slightest - or that a criminal is a human being with complex motivations and personal circumstances. For Henry, once the law has been broken, someone has become a criminal and a criminal exists only to be punished for their transgression.

These ideas are articulated particularly effectively in the final two episodes of the series in which the brothers Fielding are juxtaposed against the two brothers who lead the Royal Family, one of London's brutal criminal gangs. The gang leader, the ironically named Tom Jones, has Henry, but John has Tom's brother: it is John who ultimately treats his captor the worst by threatening and eventually torturing him until he gets the information he wants. Although it is clear that Tom intends ill for Henry, actually they spend the episode engaged in a debate about the nature of morality, justice, crime and punishment. That Tom is a man with great potential whose circumstances will not allow him to flourish in any legitimate way is something the series itself is capable of acknowledging. Henry, however, is not. Because Tom has broken the law (and the ways in which he and his gang break it are particularly distasteful - rape as well as theft and violence) he goes to the gallows with his brother, despite his best attempts to protect him: Tom's potential and the love between the brothers that mirrors the Fieldings' own are rendered irrelevant by his criminal status.

City of Vice is a complex, gritty and damn cool. More of this please, Channel 4!