OK, so I'm glad to say I'm back up and running thanks to a really great AA guy.
The first aim of course was to get the car running. He checked systems through the
OBD socket, no life whatsoever. He was struggling tbh as the car was deadlocked and it's not the easiest to get past the front seats to get to the battery in the boot. By chance he tried the rear passenger door from the outside and it opened! I never thought to try the other doors when I was looking at it
. The other rear door, passenger door and boot remained firmly locked. His initial thought was that the passenger rear door lock may have been the cause of the battery drain which makes some sense, though I never had any indication of an open or unlocked door. It certainly looked fully closed.
So, now with access to the boot and 12v battery he checked the voltage...
3 volts! He connected a booster to the battery terminals and after 10 mins got me to start her up and sure enough everything burst into life. I've never heard so many bings and bongs or seen as many fault messages and warning lights!
I kept my foot firmly on the brake peddle, put it in hybrid mode, hooked it into drive and blipped the throttle and the ICE started up. He checked the charging rate which looked good. After a good 20 minutes or so he hooked his booster/charger up to the terminals in the engine bay and restarted the car (not the ICE). This kept the 12v battery charging whilst he looked through the error codes.
With so many fault codes on his
OBD reader he tried to reset them. But his machine was unable to clear the them so I thought I'd be booking it in with the dealer. Anyway, he said there was something else he could try. He disconnected the 12v -ve terminal and connected a power drain (actually an electric tyre pump) to the -ve cable and the +ve battery terminal. This drained any remaining residual current out of the car which, he described as giving the cars systems a hard reset.
On connecting everything back up we started the car back up and once everything settled down all the fault codes disappeared. I had to select 'Dave' as primary user and all my settings were exactly as I'd like them so all good. I've been out for a decent drive and normal reality has resumed
.
I will of course have to keep an eye on things to see if I get any further 12v battery drainage but, if I can get into the damn car at least I'll be able to get it going myself.