I have for the second time left a low drain item (phone charger, gps lead) connected to the 12v socket, not just overnight but for 2 weeks or more. The car has not been used much over the last year.

is there a way using VCDS to program the socket to work ‘ignition on’ only?

BTW the RAC have been very good testing & sorting out a new battery.

Nope - you'll need to change where it gets power from