Here’s a message for the political class. Put aside the polls and focus groups; if you really want to know what’s going on, take a good look at the bestseller lists. On both sides of the Atlantic a new form has come to dominate mass-market fiction: the religious thriller.

Of course the 800lb gorilla of the genre remains The Da Vinci Code, set for a fresh surge of record-breaking sales as the movie adaptation starring Tom Hanks and Audrey Tautou has its premiere next month. But the Dan Brown blockbuster does not have the field to itself.

The Last Templar by Raymond Khoury and Steve Berry’s The Templar Legacy have stormed the US bestseller lists, centring on a specific aspect of Brown’s story, with their shared focus on the Knights Templar. In Britain, Kate Mosse’s Labyrinth, with its own take on the grail mystery, was voted “best read of the year” at the British Book Awards last week.

So what’s going on? Until now thrillers have fitted a reliable pattern. Those that didn’t deal in serial killers and gore grappled with the great political ideologies of the 20th century. Nazism was a favourite theme, from Marathon Man and The Boys from Brazil to The Odessa File and Fatherland. Or there was the long cold war against communism.

The classic of the form was John le Carré’s Smiley series, wintry tales of rival spymasters; Tom Clancy navigated the same waters a tad less subtly. In the post-war era the servants of Moscow were the stock villains for any drama that required an unqualified bad guy. Sometimes there were variations — witness Michael Caine’s uncovering of a wicked plot by the Albanian secret service in The Ipcress File — but the essential faultlines were the same.

The 1970s saw a fresh sub-genre, the paranoid conspiracy thriller. As Americans came to realise their own governments had lied to them over Vietnam and Watergate so they queued up for Three Days of the Condor or The Parallax View, brooding stories of enemies within.

If thrillers provide a useful window into the concerns of the hour, that’s hardly a coincidence, for they rest on conviction. The action will often involve people engaged in extreme acts — killing or risking being killed. The reader has to believe in their motivation.

A small grievance or a mild concern won’t do it: they have to be unshakably certain that something larger than themselves is at stake. Why else would they throw themselves off a moving train or jump into a freezing lake? For the decade after the fall of the Berlin Wall, there was a motivational vacuum: with no communist menace to halt, what might drive the action? The gap could be filled with post-cold war stories of rogue Russian nukes, or else SAS tales of derring-do, courtesy of Andy McNab and Chris Ryan. But a cause big enough to motivate both heroes and villains, that was missing.

To find it writers have gone back to the beliefs that predated political ideology: faith. Now their characters are driven not by a desire to advance or thwart this or that political system but to uncover the truth of some of mankind’s oldest creeds.

It works because it seems to ring true. We cannot imagine many people in today’s world endangering their lives for a particular view of political economy: but we know they would do that, and much more, for their religious faith. In this thrillers are merely reflecting the new driving spirits of the age. Where once the heart of the conflict was ideology today it is religious belief.

In its most direct and violent form it is the war of Al-Qaeda against the West. But this clash keeps finding other expressions, too. It might be the international furore over the Danish cartoons of the prophet Muhammad or Shabina Begum, the Luton teenager, and her legal fight to wear the jilbab to school. What these episodes reveal, one after the other, is the driving power of faith, a fervour few, if any, political movements can rival.

And it is not just Islam. In the US Christian activists are putting their convictions into the public realm. At the extremes that has meant violence, with shootings of doctors willing to perform abortions.

Christian conservatives have spent the past few decades, and millions of dollars, promoting their world view, whether by lobbying for creationism on the school curriculum, pressing Hollywood to project “family values” or seeking to become a decisive bloc within the Republican party.

Of course, politics still motivates millions, whether it be radical nationalism or passionate environmentalism. But when it comes to a force that can and does push people to the very extremes of human conduct then, wherever you look, it is often religious faith that is involved.

I suspect that is what has drawn thriller writers to dust down their ancient theological texts.

It certainly played a part in the conception of my own novel, which involves a modern-day collision of ancient faiths. For religious belief can power a story in a way the old ideologies cannot match. If writers and readers are turning to religion, that might be telling us something about not only the state of popular fiction — but the state of our world.

Jonathan Freedland’s The Righteous Men, published under the pseudonym Sam Bourne, is published by HarperCollins, £10