There is an article in the Vortex magazine (pdf) and interview with cast member Alex Mallinson, with a small photo of the cast, which gives great background to the audio recording.

Colin and India are warm and mischievous leads while the guest stars, JJ Feild, Alec Newman, Sam Clemens and Andree Bernard quickly launch into ribald banter and Nick just encourages the chaos.
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Suddenly it’s my turn to play a Geordie squaddie under Sam Clemens’s deranged Sergeant Atherton. Later on, in the pub, we swap stories about parachute jumping and it so happens that JJ, Sam, Ken (Bentleeey!!!) and I have all done it. There in the booth I experience the same sense of trepidation as I did in the plane, asking myself if I can go through with this; then Nick says “Cue”, the terror vanishes and I just enjoy the experience.
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One last job to do before we wrap, so Andree, Sam, JJ and I troop into the booths and prepare to record the wildtracks. No cocktail parties thank goodness, instead we scream ourselves hoarse baying for blood, being machine gunned and setting upon hapless soldiers. It turns out that JJ, star of screens both big and small, hasn’t done radio before and has a look of genuine glee after our cathartic efforts.