It actually looks like Sainsbury's implementation of ZAPP might be quite good - you'll be able to scan items with your iPhone as you walk around the store, pay on your phone, and just walk out! All without going near the checkout.
Of course, it would be nice if they support in-app Apple Pay for that...
how many stop and searches are there going to be from security looking to make themselves relevant?
Thing is the moment you pay for your goods, the moment money exchanges hands the goods are yours and you don't have to do anything the security asks. They have no power except to accuse you of theft and call the police. If you open your bags its voluntarily. I can see many people getting fed up with stop searches and saying bugger off.