Hi Andrew,
Many post war Villiers engines had separate HT leads that screwed into the magneto backing plate with a bakelite fitting. The connection between lead and coil was via a spring loaded contact. If the bakelite fitting is still in place, unscrew it and see if the spring and contact are still there. If so it may just be case of attaching a length of new HT lead (there will be a little screw that connects the contact to the wire). If not, the lead with fittings can be obtained via a number of suppliers there is atlas one in Aus but there are a number in England.
If it is a C25 engine, then it will have a different arrangement where the HT cable is cast into the coil assembly. Again, parts can be obtained from the same sources.
Overall, these engines are fairly strong and are reasonably straight forward to work on.
Kind regards,
Sir Chook
