We don't have a local B&Q but the other week I was working close to one and went in to purchase £140 + of electrical equipment.
As the till lady was scanning I asked for a couple of carrier bags and was told I would have to pay for them.
Said to scanner, suggest you put this lot back on the shelf, I ain't spending over a hundred pounds and then being charged for a couple of bags.
Then walked out.
Done exactly the same thing - lady told me "it's not discretionary", so I told her to put them back.
This nonsense will become law in the near future.