In another post on here I had other issues.
Part of it was the car alarm going off and not stopping. I disconnected the negative on the left hand battery which stopped it. Then big mistake I thought shut the boot manually.......eek how can I get into an electrically operated boot with now no power.
Well when the break down guy came to take the car to the dealers he knew a trick.
Open the bonnet/hood, left hand side were the windscreen washer fluid filler is, open up the scuttle cover, on the side closest to the engine bay there is large electrical connector with a plastic cover, open the cover, connect a jump starter booster or battery, positive here and earth on the engine somewhere and voilą, go to the drivers door pull the boot /trunk switch and you are back in!!
This may have been mentioned before, but hey, it was a new one for me.
Nigel.

 

It's funny you posted this, I was just today thinking as I passed a car getting a jumpstart that I don't think I'd try it with the Bentley, although yes, I could use the under-hood terminal to do so. Anyway, I was just musing about what I'd do if I ever had to jump start and I read your piece and it all came together. I'm certainly not running jumper cables into the main battery area.