Not every Tesco has SIM cards. But increasingly more of them do.. You pick up the SIM and if you present it to the human at the top-up counter and buy at least a 10 pound fill-up coupon, the SIM is free. After you install the SIM and download the credit you purchased, it is important that you then order a "rocket pack" or you will be charged for data at a crazy rate. To get a rocket pack, before making ANY call or using ANY data, call 282 from your phone. I learned this the hard way on my last trip.

Some SIMs automatically note that they are rocket pack SIMs but if it says on the SIM that it gives triple credit, it is not and you must call 282 right away while you still have the full 10 pound credit.

Rocket packs expire after 30 days.