Thanks for the replies folks.
I’ve been resurrecting VAG cars for 30 years and never seen anything like this.
First thought was battery, Cliff, as it looked like it’d been there since WW2, brand new one installed.
Carpets are dry and there’s no indication of ever having water ingress.
Scanned with Vagcom/Rosstech and at an Audi dealership
I’ve multimetered every wire l could find and there’s no continuity issues.
Fuses changed just in case, as we used to say, “gone dry”, new relay fitted too while l was there.
Here’s something new that’s literally just popped up for the first time. EPC Fault - See owners manual.
Im now wondering if it is an ECU fault as Steve says.
Thank goodness l kept the old Golf 4 PD130 just in case of emergencies. Hasn’t broken once since l bought it new in 2003..