I popped into a large Tesco today and the woman serving me refuse to let me pay by card because the transaction was less than £1. I asked her when that started and she said it's been that way for years and she'll get in trouble if she accepts the card. She gave me this story about the banks being upset with small card transactions. She asked me if I had the cash but I didn't and offered to go to the cash point. Then she made me get cash back so I could use the card.
Sometimes I just pop in for milk or a doughnut etc on my lunch break and use my card at the Self Checkout. I mentioned that to her and she just shrugged and muttered something under her breath.
Very odd.