Spooks, BBC One

At the end of series seven, our tight-lipped MI5 squad risked designer shoe leather and impeccable coiffure to defuse a Russian atom bomb in London, and their boss Harry Pearce (Peter Firth) was kidnapped by dubious Russian agent Viktor Sarkisian. Hence series eight began with the hunt for Harry, whisked (unbeknown to his underlings, who expressed their concern by smiling even less than usual) by helicopter to a mansion in “Moscow on Thames”.

One assumed that Harry would in due course be restored to his futuristic glass-panelled office, where he likes to drink whisky and reflect on the deaths and betrayals which weigh heavily on his soul but which he won’t discuss out loud, though a twinge of doubt lingered. This was due to the historically punishing mortality rate among Spooks’ leading characters. Rescued he ultimately was, but the trade-off was the loss of venerable analyst Malcolm Wynn-Jones, a Le Carré-esque figure from the old school of dogged, fine-mesh intelligence work. Malcolm was very tired, he told Harry, and wanted to retire to the coast to read books.

Meanwhile there was a reshuffle among the Americans, with glamorous CIA agent Sarah Caulfield (Genevieve O’Reilly) arriving in London to replace the despicable Libby McCall. So despicable, indeed, that not only was he a Christian Fundamentalist, but his murky past proved to be the key to Harry’s disappearance. And finally, there was the return of Harry’s platonic love interest Ruth Evershed (Nicola Walker), who vanished down the Thames on a barge a couple of seasons ago, but was forced to abandon her new life in Cyprus because she was tracked down by bad guys who knew she knew too much. This didn't save her from cruel abuse by the sinister Indian spy Amish Mani, who tried to wrest vital information from her by having her new husband killed while she watched his death on TV. The poor woman was inconsolable, but obviously she'll have to turn to Harry for support.Quite what has made Spooks so durable remains difficult to define, since in many respects it’s utter codswallop. The climate of terror which has enshrouded us since 9/11 doubtless plays its part, and perhaps also the fact that Spooks is a rare remaining vestige of a lineage of action series that stretches back to Sixties classics like Danger Man. Harry is a direct descendant from earlier authority figures like George Cowley from The Professionals or The Sweeney's Chief Inspector Haskins, and if they ever do bump him off they might as well turn off the computers and lock up the Spooks studio for good, because there isn't much else holding it together (Hermione Norris, Richard Armitage, pictured above).

For all its deployment of storylines urgently plucked from the current news agenda - last night’s episode concerned a secret stash of weapons-grade uranium which had been smuggled into Iraq in order to be “discovered” and thus justify the Anglo-American invasion – these usually turn out to be mere background noise. Basically Spooks is about hilariously artificial encounters between the characters, clumsily manufactured dramatic tension, and a denouement involving someone being prevented in the nick of time from detonating something/killing somebody/triggering a global economic collapse.

But Spooks does have one notable distinguishing trait, which is the way it portrays MI5, bizarrely, as an autonomous organism which follows its own agenda, often dictated by Harry Pearce’s moral conscience (an unpredictable instrument at best). Though Hermione Norris’s Ros Myers spends much of her time visiting the Home Secretary (Robert Glenister), who thinks he has some control over the unit, they always make a point of ignoring his instructions.

Ros herself is so exasperatingly unconvincing that she makes Austin Powers look like Kim Philby, especially when she tries to affirm her reputation as a ruthless bitch by smirking at people and raising one eyebrow. Her male counterpart, Lucas North (Richard Armitage), is wasted in counter-intelligence work. He should be modelling for Hugo Boss. Despite it all, I shall of course be watching again next week.