Just wanted to give an update on this in case it is searched at a later date.

It seems it was a combination of points/condensor needing to be replaced and tacho being stuffed.

Tried another tacho I have which could go past 2500 but was stopping around 3K and jumping all over the place so I took a look at the Clubby tacho in question and opened it all up. Just out of interest I decided to flick the needle and noticed it wouldnt go past 2500 - due to the age of it, it was actually sticking at 2500 and well I couldnt really sort it out myself so bought a decent VDO tacho from ebay which was going cheap and it is working fine but the signal to the tacho is still all over the place. As per some of the above comments my mechanic recommended I replace my points/condensor or do an electronic dizzy conversion.

I will likely buy an electronic conversion kit and give that a go. Car is running fine though so no huge rush.

Thanks for the advice above!