After much reading over on Club Triupmph (they really are VERY....... knowledgable
) i finally figured out what was wrong with my fuel gauge.
When i bought my donor it didn't come with any instruments, which wasn't a biggie, so i had to by a set from Spritfire Graveyard and fit them myself.
As i had the alternator conversion i mistakenly assumed i didn't need the Voltage Stabiliser that is bolted to the back of the speedo so i took it off
After a quick check with the beard-farm (this term is meant in the nicest possible way as i am in awe at some of the things they know!) , i realised that this is actually needed! And i've just put it back in and the fuel gauge is now working fine!
Although i'll have to take her for a blat later on to double check how the temp gauge is now working. I wonder if i can make it as far as Cullompton?