Hi all,
last Wednesday while driving on A1 I got parking brake warning light come up along with what has been an intermittent AHS light too. Car then go 'transmission error - selected gears only' warning too and airbag warning light etc. So, not surprisingly, in my mind, a main electronics failure somewhere (initial thought was alternator but read on). Managed to at least get off motorway before switching off and calling AA.

Cutting a 5 hour story short, the AA recovered it and it's over at garage at the moment. As car wouldn't restart and power made no difference they had to use 'sliders' to get it on flatbed as couldn't release the parking brake.
Just spoken to garage who haven't had a chance to do anything other releasing parking brake cable to get it into their premises (as was gone midnight AA had to leave outside on road). Even with power nothing responding properly (including brake)

However what is odd is that garage have stated that the vehicle isn't communicating at all (ie can't code read with OBD).

Any thoughts gratefully received......

OBD port needs power to communicate.

You appear to have a total fail of power distribution, how are the garage applying power - just attaching a charger/booster to the terminal - maybe your disconnect device on the battery has fired or failed

as I understand it, they've charged batter, had jumper on it and also swapped a different battery in ...