Hi and thanks for the reply.

I managed to remove the main drive sprocket off the shaft . It's a left hand thread fitting ...duurrr..should have figured that one , when i couldn't find a grub screw, split pin or cirlock pin.
However the main output shaft has been worn from the damaged bearing, so that needs replacing. Now the frustrating bit ! The mower service centre here in Nottingham that sells all spare parts , wont supply a shaft , unless you have an account ! Special order only , and its only £ 18 plus Vat . The bearing is a standard off the shelf job for a tenner. So now my mate has to take mower to them, so they can do the repair , and no doubt charge him a small fortune ! A fourty quid repair by a jack of all , become's a 140 quid job.

Pete.