Last Night's TV: Ashes to Ashes, BBC1<br/>Who Killed the Playboy Earl?, Channel 4

At the end of Life on Mars, as fans, and come to that anybody who happened to be in the country, will recall, time-travelling policeman Sam Tyler, fed up with the dreary, form-filling routine of the 21st century, chucked himself off a tall building and ended up in the paradise of 1973. (If only, we now think, Sir Ronnie Flanagan had managed to file his recommendations for cutting police bureaucracy a few months earlier.) And since this version of 1973 seemed to have been proved fairly conclusively to exist solely in Sam's head, that seemed to wrap things up.

But good TV ideas never die; they only get spun off into a slightly different format. Ashes to Ashes (another David Bowie reference: "Ashes to ashes/ Funk to funky") opened, like its predecessor, in the present day, though now the action is set in London rather than Manchester. The series started with shots of familiar city landmarks such as the Gherkin towering upwards and spinning around, as if the cameraman was being stretchered about the place by cackhanded ambulance men. To locate things even more precisely in time, the view took in one of Antony Gormley's life-size statues, which perched on rooftops in sight of the Hayward Gallery all last summer, looking poised to jump, an echo of what happened to Sam Tyler.

This time around, the action revolves around a woman, Alex Drake (Keeley Hawes), a psychologist employed by the police as a negotiator, who has been studying Tyler's case and knows his fantasies intimately. Driving her daughter to school in last night's opening episode, she was interrupted by a call to a hostage situation, which happened to be taking place right by Tate Modern (you get the impression this is made by people who don't actually know London but have got a pretty hip guide book). A madman was holding a passerby at gunpoint, but the appearance of randomness was deceptive. It turned out that the madman, Arthur Layton, had asked for Alex, knowing her from childhood, and knowing something about her life that she didn't. Having vanished from the scene, he turned up again to drag her down to the Thames (this time, we were across from the Millennium Dome) and shoot her. Next thing, it was 1981: the Dome was replaced by a flat patch of wasteland, there were Adam Ant posters on the walls, Ultravox were playing in the background; the women had bubble curls heaped up extravagantly on top of their heads, and the men were disfigured by floppy, asymmetric new romantic fringes. Now she was DI Drake, seconded to DCI Gene Hunt's team as he fought the drug-dealers flooding London with cocaine; and one of the dealers was Layton.

Since both Alex and the viewers are acquainted with Sam Tyler's version, it didn't take long to get up to speed. She was not really in the past, she was in a particularly vivid hallucination, which must have been taking place as she hovered between life and death. If she could pick up the clues and track down Layton, she could find out what he knew and get back to reality and her daughter. Mixed up in all this were allusions to Bowie's "Ashes to Ashes", including a scary clown from the video, who turned up every now and then to say something enigmatic and menacing.

At bottom, this is the mixture as before: a bit of pop culture, a bit of sci-fi, a bit of weirdness, and a lot of Philip Glenister hamming it up as old-style macho copper DCI Hunt. This time around, though, there's a bit more self-awareness. A couple of times, Hunt's appearance was accompanied by swelling choirs and orchestras, the kind Hollywood traditionally uses to signal the appearance of the deity, or at any rate Charlton Heston. Hunt joined in the fun: cut off from a gang of drug dealers by the Thames, he quipped, "Even I can't walk on water." The range of influences has expanded. Life on Mars took The Sweeney as its jumping-off point; this one has the same home-grown roughness – signalled mainly by referring to prostitutes, rather repetitively, as "toms" – but mashed together with Yankee slickness: a climactic shot of Hunt and his team on a speedboat, brandishing Uzis, screamed Miami Vice. I suspect a more important transatlantic influence is Lost, the show that demonstrates how just a hint of something a little bit paranormal gives a writer licence for any amount of incoherence and general silliness. Still, as David Bowie almost said, I'm moderately happy: hope you're moderately happy too.

Who Killed the Playboy Earl? was a hugely padded and over-hyped telling of the story of Anthony Ashley-Cooper, 10th Earl of Shaftesbury, who was murdered in November 2004 by his wife, Jamila, and her brother, eager to get their hands on his rapidly diminishing fortune. Peeking out from under the bombast, though, was a genuinely pathetic story, about an elderly man struggling to recapture the irresponsibility and sexual swagger of his youth (tight black leather trousers at 66? Save us all from such misjudgement), and falling into company that was seedy, and something worse than that. This could have been touching, if it hadn't been so revoltingly keen to be shocking.