Many thanks Mark, was able to get a 24mm socket today, got the flywheel off and replaced the (plastic) ring gear. Now all I have to do is replace the starter pinion.
Thanks again
Mike
I know this sounds like a daft question but I'm in France, my large socket set is in the UK and the one I have with me doesn't go big enough so I need to go buy the right socket to fit. Any help much appreciated.