Managed to get it to turn over on the starter but it wouldn't turn over against compression, plugs out it was OK.
Checked the electrical connections, all seemed OK so I dropped the starter motor.
Turned out the rear bush in the starter is missing ! Also one of the 'clockwork' springs that hold the brushes in place was broken and the post the spring attaches to was also broken.
I really need to replace the starter or at least the endplate containing the brushes.
Found & fitted a bush, bent the broken spring back into shape and bent the mounting post to hold the spring in place. When re-fitted it turns over the engine much faster but is still slow against compression.
Colin

