On my latest trip to London I have barely had to dip into cash. Instead, I have used a credit card that works simply by touching it to the payment terminal. So long as the price is less than a certain amount, there in no need for a PIN or a signature. I started to pull out my pounds for a £2 purchase at a convenience store, but the proprietor pointed me to the terminal and asked, "Card?"
I've used so little cash that I haven't had to use an ATM and still have most of the pounds I had left over from my last trip. This is a big difference from just a few years ago.