MATT LYNN used to be a ghost. Fittingly for an author who makes his living writing about the clandestine activities of special forces, he used to inhabit the shadows of the literary world – often read but never heard of.

You might not be familiar with his name but if you like military thrillers the chances are you've already read a Matt Lynn book.

Until last year he was a ghostwriter, an unsung hero who was paid to write books credited to a famous “author”.. As with all military “black ops” ghost writing falls into the deniable category. Matt could tell me who he used to write as, but then he'd have to kill me.

A financial journalist by profession – he still writes a column for Money Week and is a regular contributor to The Spectator – Matt got the ghosting job after penning a couple of moderately successful thrillers.

“An editor at Random House asked me if I could try my hand at writing military adventure. My guy had already written a couple of books which they got someone or other to write. He'd got fed up with it, so they asked me to do it. I'm pleased to say they did a lot better when I took over.”

Ghost writing is a growth industry. These days it seems every minor league celebrity has a novel within them – minor issues like being able to write are no bar to success. The UK has a cottage industry of professional writers who don't mind their work being passed off as someone else's.

But how does it work? “You basically write the book. I'd get something along the lines of “OK, Matt, we're in Afghanistan and there's a huge explosion and... you take it from there.” I'd usually go and stay with him for the weekend. We'd go through the story together and we'd talk through the technical bits. He's particularly good on that.

“Because all the ex-SAS guys hang around together, if I needed to know how to board a speed boat, for instance, he'd get on the phone to “Joe” and “Joe” would come over and tell me what it was like.”

Of course, some celebrities are more honest about their writing abilities than others. Naomi Campbell once confessed she hadn't read a word of the “blockbuster” that carried her name, Katie Price famously said “I don't know if they've mentioned it in the book” (the book being her autobiography) and Big Brother contestant Pete Bennett, when asked how he wrote his first book, said of the experience “a posh geezer came over and asked me loads of questions”.

Not that Matt minds his association with a famous name. He may have done the writing but his subject helped in other ways: “It was a great education for me because if you're a journalist it's quite hard to get close to special forces. It's a closed world and they're not that keen on talking to outsiders.”

The collaboration also gave him the idea for a series of novels published under his own name which began with Death Force last year. He may not have reached the number one best-seller spot, as he did three times when impersonating someone else, but the series has been successful enough to establish him as a name in his own right.

Death Force sticks closely to the conventions of the genre: a masculine hero with a strong moral compass who's a comforting affirmation of traditional values in troubled times, a team of mercenaries seeking redemption, double-crossing establishment figures, long, loving descriptions of military hardware and action, lots and lots of action.

The title refers to a team of mercenaries working for a Private Military Company, or PMC, who take on the missions no sane soldier would shake an AK47 at.

Professional guns-for-hire have been a fact of life for hundreds of years - the Greeks helped Alexander the Great build an empire, barbarians did the same for the Romans and the British bolstered their forces, non too successfully, with Germans during the American Revolution.

Nowadays they are called soldiers of fortune, privateers who would rather fight for money and plunder than high ideals or Queen and country. In Iraq and Afghanistan they provide support and back-up to overstretched military units. Though technically accountable to international law, critics say they are often unregulated and unprincipled, getting the job done by whatever means are necessary. Perfect material, then, for an action thriller writer.

“All the ex-special forces guys I met were working for the PMCs. They'd been out in Afghanistan, Iraq and South America making quite good money. It's a boom industry and nobody has really used it as the basis for a novel before.”

America, in particular, has warmed to the idea of outsourcing the war on terror.

In the 1991 Gulf War, the Pentagon employed one PMC operative per 50 soldiers. By the 2003 Iraq War the PMC's comprised the second largest force after the US military larger, even, than Britain's contribution. Now there are a quarter of a million.

Although the Death Force are killers, they all have a higher moral purpose than their enemies. “They can't be cold-blooded killers,” says Matt. “If they were, they wouldn't be sympathetic. I ghost wrote a book about a Mossad assassin and it was really hard to write a sympathetic assassin. The people they are fighting have got to be the bad guys.”

Each novel takes around a year to plot and write and comes in at around 100,000 words (approximately 400 pages). Although he's never been to Helmand he has visited Kabul and tries to get first hand experience of the weapons his characters use (although a thermobaric bomb, a weapon just one step down from a nuclear bomb in destructive potential, proved understandably hard to track down).

Critics say the genre jettisons characterisation for thrills but Matt reckons it merely reflects society: “I think we all have much shorter attention spans. Whether that's because of the internet or 24-hour news or something else I'm not certain but readers want to be thrown into the action. They aren't willing to invest half-an-hour as the suspense builds.

“People think of them as very simple stories. In some ways they are easy to write, because you can always just have another gunfight if you want to spice it up a bit, but they've got to be interesting and if you don't care about the characters it's not very interesting.”

Publishers love them because they have tapped into a part of the market previously dormant – the 20-something male reader.

Thirty years ago they were buying James Herbert horror, George Gilman Edge westerns and Sven Hassel WWII adventures. Somewhere along the way publishers lost the market and today's young men prefer Medal of Honor on the PS3 to reading a 400-page novel. Andy McNab, Chris Ryan and their contemporaries have helped the industry reconnect.

Matt has a simple formula for his stories: “I like to start with a big fight. There should be lots of interesting kit. The characters have got to move forward and there's got to be a twist. A mission can never be what it seems, there's got to be a surprise.”

So far it's worked a treat. Two Death Force novels are already out, a third, Shadow Force, is due next year and he's nearly finished the fourth (Ice Force) due for publication in 2012.

It's a long way from his “day job” writing for the finance pages. With the recession forcing countries to pare back defence spending could there be any overlap? Perhaps, not: “They are very different genres. You can't suddenly have a long exposition of the sub-prime market in a Death Force book; it just wouldn't make any sense.”

As Matt says: “It reassuring for my readers to know that there's always another gunfight just around the corner.”

* Death Force and Fire Force are out now. Shadow Force is published in February. An audio-book of Fire Force was published by Isis Audiobooks this month.