[Arran]

It's probably a baked on enamel, they didn't have epoxy paint in the 1940s and 50s. I don't know what Formby's paint and varnish remover has in it but if it isn't methylene chloride based get some that is, I have found that you have to go at it with fine steel wool while the stripper is wet. Another solution may be to try methyl-ethyl-keytone, outside with chemical gloves. One chemical that I have also heard will strip paint is brake fluid, dot 3 to be exact.
Regards
Arran