Much thanks has to go out to Jules, with whom I got in touch over this issue.
As he's not too far down the coast from my abode in N Wales I was able to drop my Conny in with him to diagnose the issues.
Ironically on the day I drove down there were actually no problems with power delivery at all
Fortunately Jules has the kit to investigate these matters, the fuel pressures were coming it at approx 210 psi(?) and we replaced both the Under Bonnet and Fuel Tank pumps.
Pressure delivery is now around the 270 mark, and there have been no further issues at all
He also discovered a worn drop link, and was also able to track down the faulty wiring on the NS Headlamp
https://the75andztclub.co.uk/forum/s...d.php?t=303510
And ran in a new connection for me.
Also able to get a few other bits and bobs resolved :-)
So if you're in need of help in North Wales, Jules is definitely the man to go to