Hi Fenders
Yep, mine's done exactly the same (and if you find a UK supplier, please let me know!). If you look at the inside face of the lock, you will see a hole with 'teeth'. Stick a flat screwdriver in it and turn one cog against the other (you'll see when you try it). It compresses a spring-loaded thingummy that holds the lock in place in the acrylic and allows the assembly to be slid out. Dead easy once you've done it the first time. I've been too busy to look around for a new once since I cracked mine but very gently prised the crack slightly apart and ran some superglue in there, which capilliaries quite a long way and helps support the thing until replacement. I was able to drill a little hole to stop the crack lengthening but it looks like yours goes edge to edge. Good luck.
Happy New Year, all...
*edit* just looked at your pic close up - you can see the teeth below the thumb-slider. Also, looking at the crack, I'd reinforce it L-R with a luggage strap to stop the side breaking off if the spring snaps back, it's quite strong and the driver can slip.