Was the alarm "buzz" / high pitched whine you get when there's something not quite right, so tried to switch off with fob, nothing, back into house, dig out immobiliser "key" and try that, nothing. Try to flash headlights, nothing, notice interior light is very dim - Aha, something's drained the battery and alrarm got upset.
Go back into house, get keys for vectra, pull that up onto the front path / lawn to get jump leads hooked up, leads on, indicators flassh, alarm goes off proper, reset with plipper, start it up (I have real heavy jump leads made from welding cable) and all seems fine. Walk round car and realise the brake lights are on!! AHA!!! Brake light switch has left them on overnight (aklthough convinced they weren't on when I left the car) and drained the battery, pull the switch out and find that it works fine, but adjustment must have slipped.
And all before walking the dog and leaving the house at 8 o'clock
Hopefully it's OK now!
Oh what fun, just like Classic Minis, give you a daft problem whenever you think they're going great!!