In message ,
harry writes

From memory the fuel gauge sender is under floor mat in the boot/behind
rear seats. Just a float and a rheostat.

Thinking aloud here. Were I to disconnect the wire from the tank
sender, and short it to earth, assuming wiring and gauge OK, the gauge
will then read 'full', confirming the fault is with the sender?

I'll check the fuse first!

--
Graeme