Well this week I've been busy stripping the Mk3 Commando and checking it out for the engine problem. My prognosis was correct, the foot has come off the end of the cam follower as you can see in the photo, the half moon thing should be firmly stuck to the follower and not lying in the bottom of the crankcases where I found it. There was also a broken top ring which luckily hasn't caused any damage apart from the obvious carbon build up on the head. So all in all not a big disaster, the cam seems fine and I've decided not to split the crankcases to rebuild the bottom end as it doesn't need it and with the quality of new parts these days its better left alone with the bits that have lasted the last 33 years.
Some fettling and much cleaning to be done before its rebuilt, hopefully next week!