I've held off tackling some of the smaller jobs still on the 'to do' list, mostly because of a lack of time but also partly because I just want to drive the car.
I have had another crack at the fuel gauge having reworked my adapter circuit. A check with a multimeter showed that the sender was indicating a full tank even after 180 miles of driving. Clearly there was a problem in the tank, so it was out with the boot floor and off with the pump retaining nut. The top and bottom parts of the pump clearly weren't aligned properly, interfering with the movement of the sender.
I don't know if there is a recommended technique for installing the pump, but the compression spring between the two parts makes it really hard as you are always fighting spontaneous dis-assembly. This time I looped a length of wire around the assembly to hold it together whilst I was inserting it into the tank. The wire came out easily when required and the sender is now indicating empty, as is the gauge.
Here's hoping it's finally fixed!