Beware of the automatic checkouts. Someone I know got to the end of her scanning and was asked by the machine, how many bags she had used. As you used to get points for using your own bags, she pressed 2 (she had brought 2 jute bags with her) and then the total showed up.
When she had paid, she realised that she had been charged 10p for two plastic bags, not credited with points for using her own. It seems that supermarket no longer gives you points for using your own.
She went to customer services who reluctantly refunded her the 10p.
If I'd been next in the queue I'd have offered her a quid just to fvck off.