But that worked because chocolate is very recognizable as an ingredient. Palm oil isn't, and it's in everything. Perhaps a similar certification process might help, but when you buy something that doesn't carry the logo you'll still have to check the ingredients list because often you have no idea if palm oil was used or not.
I'd find it honestly difficult to buy lower-quality chocolate than Cadbury's. No wonder you can't find it in most of Western Europe - only Brits tolerate it, mostly because they had little else "back then" (pre-EU accession).