Thanks guys, In some ways that's infuriating, as i have spent hours looking at Lathes.co.uk, but i think "cant see the wood for the trees" covers that! 
I was about to ask what an earth a back gear is for, but then I googled it (basically going slow!)
( **LINK** 
Heppel, cheers, I was absolutely just about to try to use it to lock things up. I will re-read the stuck chucks thing, BTW is the backplate a normal thread (as i can easily take the chuck off, it the base that's stuck)? So I want to go anti-clock, this seems logical, as the lathe spins anti clock (towards the user), so when it spins it wont undo it? (or did i just confuse myself?)
Bazyle, thanks, you are clearly right, my lathe looks like a mixture between a 4C and a 4R, So the knobs engage the back gear. (I also looked my stand up)… This means i am no nearer to locking the spindle. But at least you showed me something else i did know! 
I am assuming if the front and rear oil seals basically just leak the oil through, that you live with it, I assume the seals are very much not available anymore?
(Thanks admin, for approving my post and fixing my links to the pictures.) 