Finally got around to looking at this and picked up a second hand Condenser with the right fixing and dimensions. Cleaned the points & wired it back up as it was originally but still no spark. First thought was the Condenser was duff, but I did think something looked odd when I cleaned the points, so I whipped the flywheel off again. The metal strap that tensions the points was earthing out where the wiring from the coil joins it. I put a small piece of roofing felt between it and now have a lovely spark. It now starts & runs lovely, so it was the Atom module that was causing it to over advance the timing. The previous owner probably didn't spot the earthing issue, so fitted the Atom module & created an even bigger problem.