Well, finally we have the Commer engine running!
We have literally tried everything so thanks for all sugestions. In the end we removed the starter motor as we thought it may be taking too much power resulting in a poor feed to the coil.
But, when we bench tested it we found that although she spins up the engaging dog didnt travel far enough, so cleaned and oiled etc and we got the right amount of travel. We refitted it but firstly checked the ring gear for tooth wear, it was fine.
Next we connected everything back up and now she was turning over at a really good speed but still not even firing. So we checked the spark at the plugs and it was very weak, then at the contacts and this was good. So, we took a look at the sprung graphite in the cap and we found its movement very small. So, I had a dizzy from one of Hillmans on the bench and we changed the graphite over. This time with everything reconnected she fired straight away on full choke, not only fired but stayed running. Lots of relief and plenty of smiles!
We have to now fit a new downpipe gasket and replace the brass nuts and then hopefully she will run with no choke, at present you can hear her sucking air in so obviously messing up the mixture.