Thanks for all your help chaps, glad to say its fixed!
I removed the gearbox assembly from the lathe and had it all in pieces and still couldnt figure out what was wrong until i really tried to twist the gear on the shaft and there was some movement, it felt fixed in my hand but under enough load i managed to twist it, it had been glued in previously by somebody and so it was spinning, there were no holes in the bronze bush for attaching pins, so i had to drill some and make some pins, which i can do now because i have a lathe! haha.
https://www.dropbox.com/h?preview=VID_20...113537.mp4
I removed the gearbox assembly from the lathe and had it all in pieces and still couldnt figure out what was wrong until i really tried to twist the gear on the shaft and there was some movement, it felt fixed in my hand but under enough load i managed to twist it, it had been glued in previously by somebody and so it was spinning, there were no holes in the bronze bush for attaching pins, so i had to drill some and make some pins, which i can do now because i have a lathe! haha.
https://www.dropbox.com/h?preview=VID_20...113537.mp4