Full marks for that suggestion, Stuart: My modification was to lay a meths soaked (well soaked) cloth over a section to let it soften, scrub away with wire wool, then wipe down with a (second, cleaner) meths-soaked cloth and a final wipe with paper towel. Took a good few hours to do one door's worth of architrave, but got it done. House now smells like all the local tramps have been over for a party of course, even though I did it in the covered sideway...