I think I mentioned this last year, but it bears repeating: my UK publisher, Orbit, have been working on bringing some of my books out in Audiobook formats. (For licensing reasons, the US audiobook versions aren't sold in the UK.) The Rhesus Chart and The Annihilation Score are now available for pre-order in the UK (and, I assume, EU) as audiobooks from Audible; they'll be released in June, and hopefully subsequent Laundry Files books will be available as audiobooks faster.
Note: See CMAP: "Why can't I find audio editions of your books in the UK?" for more information on this. The first two novels have been available for a while; from book five onwards they should be routinely available from now on: I've no idea whether books 3 and 4 will ever be recorded (it costs a lot to prepare an audiobook and as these books have been in print for several years there's some question over whether they're commercially viable).
This is very good news. I love audio books for long car or train journeys and I thoroughly enjoyed the The Atrocity Archives and The Jennifer Morgue. I can remember exactly where I was heading north west on the A272 in Hampshire when I heard "neuron" instead of "neutron" and my brain wobbled a bit.
Also, The Annihilation Score is already available (and now on my machine).
Would an American voice be a negative on the UK audiobook?
I'm pretty sure it would -- especially for a book with a first-person British narrator PoV.
(For "The Annihilation Score" Orbit ran a couple of voice samples past me for approval. Both by female voice actors with a slight Scottish burr -- because the book's from Mo's viewpoint.)
Incidentally, aside from having no real use for audiobooks (I don't commute to work or drive much), I can't listen to my American audiobooks because of the fingernails-on-blackboard effect of the wrong accent.
The American audiobooks for The Laundry Files so far have had an Englishman reading them, Gideon Emery. He's pretty good at switching back and forth between character accents. I can't vouch for the accuracy of his UK accents, but he doesn't make me flinch when he reads Americans.
It's interesting to compare the UK and US versions. The UK version sounds to me like what Bob actually sounds like (more nerdy and self-conscious than snarky), and the US version sounds like what Bob wants to sound like (quippy like Bond).