Overheard in a shop today (Robert Dyas if it matters)
"Would you like a carrier bag madam"
"How much are they"
"Our carrier bags are free madam - they don't have handles so we don't have to charge - but they are plenty big enough for you to get a good grip on the bag"
I cant see it working for Tesco or Sainsbury but I wasn't aware this loophole existed......