As I've always understood it, methylated spirits and denatured alcohol are basically the same thing. Ethanol with some methanol added to make it undrinkable. In the UK it also has pyridine to make it smell and taste unpalatable, and a purple dye. I've wondered in the past whether the purple dye would affect the colour of shellac. Any UK woodworkers know whether our normal purple meths is OK for mixing shellac?
It is possible in the UK to apply for a licence to buy small quantities of industrial methylated spirit (IMS) which has no dye or pyridine.
As for drinking shellac - well I'm sure that's not advisable, especially if it was mixed up with toxic meths! But once dried it's edible, they use it in the food industry.