I was offered an upgrade to Club Europe via MMB on an Avios ticket I purchased. I called up BAEC and asked if accepting the upgrade offer in MMB on an Avios ticket would get me the tier points for Business. The agent said yes. Anyway I didn't get them (understand why from Flyertalk) but I challenged BA on this. They listened to the call and agreed I was incorrectly advised and they posted the J tier points and Avios into my account.

So it can be done if mis-sold!