I was going to post pictures but I`m currently out on work...I did manage to repair it and nothing was broken. With some observations I found out that the little hair spring wasn`t applying any pressure onto the little ratchet like piece that it meant to push to take up the backlash. Equally, I couldn`t figure for quite a while how the spring could possibly positioned to engage it. It was simply a case of pushing the ratchet piece (I don`t know its real name, but the piece with the rack teeth that apply move the gears) and finger to one extreme side, the slipping the cover on then moving it back a fraction to engage the spring in every position from that extreme point. I have a feeling that when working on my lathe, I knocked it and the finger hit the bench which I can only presume caused the hair spring to come out of position. It just needed putting back again.
I didn`t think I could possibly have fixed it that easily (once I`d realised what to do) but I`ve really given it a good test and used it a few times and it seems to be working perfectly. Maybe I was lucky, but it certainly is fixed!