Fuel Gauge

I don't think that you need to do that. Get yourself a six-pack of cheap continental lager, a phillips screwdriver and a sunny saturday afternoon (most difficult bit around here, I know). Then remove the piece of black plastic trim that holds the rear of the carpet in the boot area and fold the carpet back. You will see a lid held with four screws. Remove screws and access underneath the lid. You will find the fuel hose, fuel breather, etc. Remove the clamps and undo the hoses. What you see there is the sender and fuel intake which is I believe screwed into the tank proper so to undo it you have to turn it anti-clockwise. You don't need to empty the tank, just refrain from smoking while you do this.

Then inspect the sender. It can be full of diesel muck which prevents the float from moving freely. Clean up with clean diesel and refit. It should be OK. If it is you owe me a six-packer. If it isn't I am sorry but I am a Chartered Accountant, not a mechanic so I cannot be blamed for not knowing, can I?