Most people fall asleep on trains; it's something to do with the soporific effect of the motion, the gentle rocking over the clacking tracks that lulls folks into a snooze…but not me. Nah, I can't doze on the 5.15, no matter how hard I try. For some reason, the world rushing past outside my window sets my mind turning. I've come up with some of my best plot ideas on trains, so I suppose it was inevitable that I'd write a story set on the rails - just what I didn't know was that it would star the future's hardest lawman in a high-speed race against time to stop nuclear oblivion…

Judge Dredd: Dreddline marked a number of firsts for me; my first time working with Big Finish, audio masters of Doctor Who's time-travelling adventures; my first chance to write a radio play script; and above all, my first dip into the world of 2000AD, a comic that I had grown up reading. Back in 1977, I'd never have dreamed that one day I'd get to put Old Stony Face through his paces, and the opportunity to visit the world of Mega-City One was something I just couldn't pass up.

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Toby Longworth (Judge Dredd) and ace sound technician Andrew Swann have a "creative disagreement"...

During the latter part of 2002 I'd pitched a few ideas to John Ainsworth (producer on the 2000AD Presents series) with hit-and-miss results, and when a plotline we'd been wrangling with fell through in development, John approached me with something that he'd been trying to make work but hadn't had the time to develop. He called it 'Boom Train', "a story entirely set on the Zoom train that goes between Brit Cit and MC-1," He wanted a climactic ticking-clock narrative, something that conjured up memories of Thunderbirds adventures, and something that could be told in real-time, just like an episode of 24. I jumped at the chance. We tossed around ideas, we talked about classic railway movies like Narrow Margin, Murder on the Orient Express and, uh, Under Siege 2, and the story came together; Judge Dredd would be escorting a prisoner on the transatlantic zoom, only to find himself involved in a threat to blow up the train - and the whole city!

Dreddline's story went though several changes before the final script was set. At first, the journey went from MC-1 to Brit Cit, not the other way around, ending with the catastrophic nuking of Bristol; then the storyline was retooled to serve as a direct sequel to David Bishop's earlier audio story Get Karter!, but delays in approvals slipped it back (although the story still retains a few key connections to Bishop's script); an overly talkative Lawmaster got trimmed and jokes about toilets were tossed out; but at last the text was approved and recording went ahead one chilly December day at the Moat Studio in Stockwell.

It was bloody cold that day, and because we were recording most of the heaters were off so as not to affect the microphone pick-ups. As I sat there in the control booth, shivering in my shirt-sleeves, I looked up expectantly at Ainsworth, who was directing Dreddline, and waited for the magic to happen; we had around eight hours to lay down 70 minutes worth of story. My name is James Swallow, and this was the longest day of my life.

Well, actually, it wasn't as long as all that. The cast and crew at Big Finish were an affable bunch - no time-wasting prima donna thesps here - and they got in and blasted their way through the script. At the centre of things was the Voice of The Law himself, Toby Longworth; his gravely Dredd boomed out and snarled, gleefully picking out the in-jokes in my script as well as continuing Dredd-style comedy improv after the director called cut. "I'm so lonely," he grated to one of the perps, "You're a very handsome man. Can I touch your lips…with my lips?" And the sound of JD singing "It's like a party sometimes, it makes me wonder how I keep myself from going under…" will stick with me forever. Toby was joined by Jez James (the voice of Control) as the safecracker Philo, Kate Brown pouring on a potent mix of honey and poison as the villainous Whyte, Andrew Fettes and first-time audio actor Donovan Cary as thugs Trio and Lomax, Hannah Smith reprising her role as Brit-Judge Dalton from Get Karter! and the dynamic duo of Nicholas Briggs and Jason Mitchell as Buzz and the Conductor-Bot. "Am I the only audio virgin here?" said Donovan; I meekly raised my hand in support and he grinned. "Be gentle with us…" he piped.

Each of the actors brought the words on the page to life in ways that I couldn't have imagined; I'd pictured Philo as a slick, Han Solo type but Jez nailed him like a cross between Joe Pesci and Moe, the bartender from The Simpsons; that knock-on changed Andrew's portrayal of Trio from a Goodfellas-style punk to nasal, ratty scumbag, all wound-up and hair-trigger; and Donovan made Lomax his own with a Cypress Hill-type homeboy accent with a dash of Mr. T. For a writer, it's something that's scary and cool all at once, when actors pick up your words and start to mould them; suddenly, the whole thing has a life of its own, and you're along for the ride. I listen to the finished item now and I can't imagine it any other way; the whole ensemble fits perfectly; Nicholas's excellent 'English Colonel' voice, Jason's plumy mix of BBC announcer and David Attenborough, Hannah and Kate both veering between silky seductive tones and ranting bitch-queen sneers…it's all spot-on. I even got a chance to play a bit part myself, coughing, whining and screaming to cue in some of the crowd scenes; and herding us all with deftness and aplomb was John Ainsworth.

Of course, a big part of the accolades have to be laid at the feet of the technical guys as well; Lee Bowman and Andrew Swann mingled performance with sound effects and ambient noise to put you in the middle of the audio action. Andy, who has a sense of hearing like Radar O'Riley from M*A*S*H, didn't even flinch when I told him I needed sounds like "a cross between a bullet train and a space shuttle launch" or "six pounds of ball bearings and lit stick of dynamite in a blender". I remember musing over lunch - ably prepared by Jack Galagher, who listeners will know as Emerald Isley Riley in Trapped on Titan - about what I was learning, and I gotta tell you, it was quite a lot. From simple things, like how a single misplaced comma can trip up an actor's entire performance, to more complex issues like scene pacing and script structure, it was a great ride, and I had a ball.

After the traditional post-wrap pub visit, I took the train home. I was tired but I still couldn't sleep, so I got out my pad and started making notes. Maybe I could write something set on a bus next time…or maybe an ocean liner? Or…a blimp? Yeah…that might work…

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Lee Bowman surveys his domain in the Moat Studios control room.
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Toby Longworth (Judge Dredd) voices The Law.
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Cast & Crew (left to right): Andrew Fettes (Trio), Donovan Cary (Lomax), Hannah Smith (Judge Dalton), Jack Galagher, Kate Brown (Whyte).