Oddley
Lye is obviously used in food manufacture (It's E number is e524). It just seems to be a case of getting a food grade product.
A quick Google has produced this:
http://www.reagent.co.uk/sodium-hydroxide.html
and this:
http://www.reagent.co.uk/acatalog/Sodiu ... NaOH_.html
I'm assuming that one of the ones they list may be food grade.
I hope this helps your quest for the authentic product. Please let us know how you get on.
Phil