My daughter works as a pharmacist for Asda (and incidentally, their head office is here in Yorkshire).

Although of course they do sell the same pre-packaged stuff as all the others, the bulk packaging, and all the other recyclable stuff from the stores is put back into the empty delivery lorries and returned to their recycling depot (next to their warehouse near Junction 31 of the M62). How they then deal with it, I can't say, but at least they aren't running empty wagons. It may be that most of the supermarkets do this now.
I don't often shop in there as I have other supermarkets closer, but I was in on Monday, and many people were using their own bags (as was I), with ample opportunity to buy proper bags.
I don't know why they stopped leaving boxes out - they all used to do it - maybe it was considered a safety risk by the health and safety gnomes.

Andrea