**FYI RESULT**
Today we removed the instrument panel in the Cupra TDI (connectors were really tight, don't think it'd ever been removed before), and metered the voltages. 2 permanent lives, 2 lives that came on with the light switch. The instrument panel was only out a few minutes. We refitted it and it now all works as it should??? No explanation as to what was causing the fault, as the connections were wiggled about before removing it thus eliminating a bad connection, and that made no difference, still absolutely dead.
Below is a very similar case, and the same results on a PD100
http://www.seatcupra.net/forums/showthread.php?t=293173
I wonder if just disconnecting the battery would have done the same job?? Anyway, thats 2 documented cases, both fixed by removing the instrument panel for a few minutes then reffiting it.
I try and 
