AS THE THIRD ANNIVERSARY of the London bombings approaches, the author Stephen Leather is among those with cause to reflect on the uncomfortable relationship between the real world and fiction - particularly when the plot of a thriller becomes horribly true.

In February 2005, five months before the 7/7 suicide attacks on the London Tube, Leather's thriller Soft Target detailed a plot by four British-born Muslims to explode bombs on the Underground.

As in real life, one of them went off above ground, albeit at the entrance to a Tube station rather than on a bus. His hero, an ex-SAS man called Dan Shepherd, has more luck preventing loss of life than did the real-life security services.

“It was uncanny really,” Leather says. “I had been been speaking to a lot of anti-terror people and the emergency services and they all said the same thing: their worst nightmare would be suicide bombers on the Underground.

“Then five months later it happens. I'm watching TV and there are the same people I'd been talking to, saying how they'd had to deal with it.”

The detail in Leather's book even had echoes of the subsequent shooting of Jean Charles de Menezes at Stockwell station: “My hero, Shepherd, has to shoot one of the bombers, even though he's coming at him from behind and can't see any indication that he's carrying a bomb, but there's this voice in his ear telling him that's the man. And he shoots him, and keeps on shooting him, putting bullets into his head until he stops moving. Because that's what the men at the Met told me they would have to do to deal with a suicide bomber.”

I asked Leather, a former Times journalist, if he ever felt that the resemblance between his plot and what actually happened was so great that he might bear some responsibility? Doesn't he worry that the terrorists might have got their ideas from his work? “Never. Not at all. Terrorists don't get their ideas from fiction. And in any case, I always leave out one essential detail so that I'm not publishing a blueprint for an attack.”

Nonetheless, he feels that other attacks will come, that it's merely a matter of when not if, and that key targets remain the big symbolic ones: the London Eye, Eurostar, Heathrow. His next book Live Fire will feature an attempt to bring down an airliner: something that the IRA attempted back in 1994, but which nowadays - with more high-tech weaponry - has a higher probability of success. He insists he's not writing a blueprint, but rather extrapolating from a reality that already exists.

“There are dozens of rockets out there that the Americans sold to the Afghans or in former Yugoslavia; lots of Serbs have them. The terrorists only have to be lucky once, the authorities have to be lucky all the time.”

Perhaps it is when terrorists appear to ape exact techniques that first appeared in fictional form that the phenomenon is most worrying. In his 1999 novel, Remembrance Day Henry Porter had his villain fix murderous cenotaph explosives to a mobile phone so that all that was required to detonate them was a simple call.

The Daily Mail trumpeted: “You can't go wrong with this plot”. It was a line the paper signally failed to repeat in March 2004, when bombs triggered by mobile phones exploded on crowded commuter trains in central Madrid, killing 191 people and wounding nearly 2,000 more.

There must have been a moment, somewhere between the first passenger jet crashing into the World Trade Centre on September 11, 2001, and the instant a few hours later when a third airliner smashed into the Pentagon, when Tom Clancy put his hand to his mouth and thought: “Oh my God, what have I done?” It had been all of six years since he had brought his series of novels featuring the CIA man Jack Ryan to a blockbuster climax with a crazed anti-American Japanese airline pilot crashing his 747 into the Capitol, killing the US President and half of Congress.

Of course it is the job of writers such as Clancy to imagine the unthinkable. No one seriously believes that Osama bin Laden is whiling away the hours in a cave in the Hindu Kush with a library of the latest shock-horror paperbacks (although it is an interesting image).

Inevitably, writers who make money from our desire to be scared - albeit only on paper - are inspired by horrors that take place in the real world. But it is almost equally inevitable that some impressionable minds might be corrupted by what they read. Is a “video nasty” worse than a “literary nasty”?

Maybe we should think ourselves lucky that terrorists do not spend all their time scanning the fiction shelves for ideas. To date at least, Frederick Forsyth's nightmare in The Fourth Protocol of an atomic bomb being assembled on British soil from components smuggled in individually has not been realised. That one, however, is nowhere near as easy as he described.

Dean Koontz's Odd Thomas envisioned a psycopath wreaking havoc with bombs in American bowling halls and shopping malls. The IRA did substantial damage both to Britain's image and economy with a similar campaign but that is something the US has so far mercifully escaped.

The truth is that thriller writers exist because they exploit the horror that is out there, and not the other way around. Before we leap onto the current bandwagon of banning anything that might remotely be considered risky - or requiring that all thriller writers submit their plots to MI5 for clearance - it is worth remembering that throughout history, religious texts have inspired more atrocities than any thriller.

Gerald Seymour, who prides himself on the research that goes into his thrillers, said: “If you don't understand history, then you have simply no comprehension of anything at all.” Those people are the most dangerous of them all.

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