Sent the instrument cluster to Autotronics for repair after pulling my hair out for a week. They returned the cluster to me in alleged working order after making a repair on the circuit board, but it still doesn't work. Needles aren't moving at all and remain stuck in place, but now at 0.
Have you checked the harness connectors in the footwell, particularly the passenger one.
Pretty much all the instrumentation wiring runs through the two multi plugs on the passenger side.
Also double check the grounding points around the boot and the connections to the pump/sender unit. Under the plate in the boot floor... Four screws 
Incidentally, what work was done?
And where in West Sussex are you? I have a couple of days free next week and long term experience with TVP Omegas having owned 2 and am not a million miles from the A29/283.
Where are those grounding points in the boot you speak of?
Also, if you are still offering I'd be so grateful at this point...