Is the minister a crook? And who killed the intern?

'State of Play', 'The Deal' - there's no smoke without fire, says James Morrison, so why are conspiracy theory TV dramas making such a big come-back?

Everyone loves a good conspiracy. Time was when dossiers marked "confidential", unattended briefcases exploding and anxious ministers scurrying off podiums to escape the attentions of a scandal-hungry press corps were as much a part of the visual language of television drama as period frocks, gratuitous nudity and Robson Green are today.

In the 1970s and Eighties, contemporary TV drama had teeth. More than that, it seemed to be obsessed by the notion of espionage, or at least the implications and dangers of secrecy - and the murky double lives of those who, often reluctantly, were involved in preserving it. From the forensic investigations of John Le Carré's urbane gentleman spy George Smiley to the sinister machinations that led to A Very British Coup, programme-makers took unending pleasure in examining the machinery of the state, and the shady powers whose backstairs dealings underpinned or, in some cases, undermined it.

By the late Eighties, however, this peculiarly layered breed of contemporary drama was dying a death. As the Eastern Bloc crumbled, the Conservative Party's hegemony over British politics faded and Labour began to reinvent itself as a more docile, less radical alternative administration, the nation's appetite for serials focusing on the dubious tactics of maverick MI5 agents and plots to suppress leaked nuclear secrets was judged to be on the wane. Even the succession of sleaze scandals that engulfed John Major's beleaguered government didn't re-ignite the spark.

But now the conspiracy thriller is back. Last weekend saw the start of State of Play, the most hard-edged and timely political drama since House of Cards more than a decade ago. The six-part serial focuses on the efforts of a team of crusading journalists to unravel the mystery surrounding two near-simultaneous events: a bizarre double shooting and the dramatic death of an intern employed in the office of the New Labour chairman of the House of Commons energy committee. Penned by Paul Abbott, creator of benign crowd-pleasers like Clocking Off and Linda Green, it is pacy, compulsive, and contains enough conspiring to put the wind up Machiavelli.

All the signs are that it already has a sizeable portion of the British public hooked. Critics have praised Abbott and the talented cast, led by John Simm and David Morrissey. And while last Sunday's opening episode attracted a modest 5.2 million viewers, 500,000 switched over to BBC4 immediately afterwards to watch part two - giving the digital channel its biggest audience to date.

As if this weren't proof enough of the resurgence of the conspiracy genre, tomorrow sees the long-awaited DVD release of Edge of Darkness, the classic Greenham Common-era Cold War thriller starring the late Bob Peck, to which State of Play is most obviously indebted.

And there is more to come. The BBC already has tentative plans for a State of Play spin-off, and last week director Stephen Frears began filming another conspiracy thriller of sorts, The Deal, Granada's dramatisation of the historic Granita lunch at which Tony Blair and Gordon Brown agreed their "pact" over the Labour Party leadership.

So why now should this long-neglected genre have gained such a new lease of life? To Abbott the answer is simple: for perhaps the first time since the fall of Communism, he argues, there are "conspiracies" out there for people to write about. In this era of mass corporate lobbying and increasingly Big Brother-style media manipulation, he argues, there are more layers of deception for writers to try to peel back than ever before.

"There doesn't seem to be that much going on on the surface, but in truth there's actually so much - and it's happening all the time," he explains, citing everyone from Formula One boss Bernie Ecclestone to Enron, the corruption-ridden US oil giant, as examples of the kind of capitalist power politicians portrayed in State of Play. "It's the 'smallness' that got me when I was thinking about writing this. Politics isn't theatrical any more like it was under Thatcher, but in a way that makes it more sinister.

"The problem with the kind of dubious dealings between business and government that go on these days is that they are now so blatant that we are no longer even noticing them a lot of the time.

"I wanted to approach this with my zero tolerance hat on. I just find it really galling that time and again you hear of this company or that company winning a contract, or a place on a quango through government connections.

"Everybody accepts that big oil companies do certain things to network and win influence, and that it's 'the done thing' in the lobbying world. In episode five you've got a minister saying, 'oh, for Christ's sake, all we did was...', and it's the 'all we did was...' that makes it sound so banal, and dangerous because of that."

One feature that marks State of Play out from more workmanlike thrillers like Touching Evil, on which Abbott cut his teeth, is the fact that its main protagonists are not detectives, lawyers or criminal psychologists, but journalists. In a neat twist on the usual conventions of mystery dramas, here it is the press who are one step ahead of the police, rather than the reverse. It comes as no surprise that, while Morrissey (who plays the MP, Stephen Collins) shadowed Peter Mandelson in researching his role, Simm (the hack, Cal McCaffrey) spent several months tailing national newspaper reporters.

"There's a difference between a conspiracy thriller and a genre thriller," explains Gareth Neame, the BBC's head of drama commissioning and an executive producer on State of Play. "This does not rely heavily on action and creeping up on people. It's a conspiracy where it's about people finding out what's going on. You can see there's a difference between that and most other thrillers we've seen on TV in the past few years."

Abbott gives a simpler reason for his decision to focus so closely on the journalistic side of the investigation: it just fascinated him. "I just wanted to write something that I felt people would want to watch," he says. "Having started the story from a political angle, the newsroom side of it was what grabbed me."

Throughout the series, there are clear signs of Abbott's personal interest in the mechanics of journalism, though anyone who has worked for any length of time in a modern newsroom on a national paper will find much of his depiction, however gripping, fanciful at best. The idea of an editor ordering up "a bottle of red" as he discusses a story with a group of reporters - or allowing so many people to work together on an investigation, without apparently filing so much as a single line of copy for weeks - is a world away from the day-to-day cheese-paring reality of most contemporary news operations.

But there is much that is refreshingly authentic about State of Play, and what many viewers will want to know is if there's likely to be more where this one came from.

"I don't think there's ever been a conscious decision to stop doing this sort of drama. It's just the way things happened," Neame explains. "As to whether we do another political conspiracy thriller in the near future it all depends on the story, but yes, we're certainly looking to."

'Edge of Darkness': out on DVD tomorrow (BBC Worldwide, £15.99)