Monro tiller. Villiers mk12 coil backplate removal

Donkeys years since I worked on a Villiers but that one has been stripped fairly recently so I wouldn't expect the backplate to be stuck. It may be that there is another nut behind the mag coil, not entirely sure why you don't just undo the screws holding the coil on anyway, rather than removing the backplate. By the way, the HT lead is not attached to the coil, it ends in a contact that touches a brass thing on the coil. Be very sure it isn't just the points needing cleaning and gaping correctly, before changing the coil. 9 times out of 10 it is points, when the engine won't spark.