The bad news is I'm typing this from Bristol after BadgerLAN. My car saw fit to stop central-unlocking, which I believe is also the mechanism for disabling the alarm and immobiliser. We packed up late enough to have already missed the last train home, so we're now stranded in Bristol. I'm going to get the train back to Cheltenham tomorrow morning and bike into work (luckily for me I have two vehicles).
I've left the battery and the horn disconnected, I've checked fuses and tried all the central locking tricks I can think of but nothing has worked. I've let work know I'll be late. Ah well I'd better get some sleep...