The Stingrays, which mimic cell towers to intercept mobile traffic, haven't proven all that useful to the SPS though. As mobiles have grown more sophisticated, and network technology has quickly moved from 2G through 3G to 4G, the IMSI catchers have become less effective. More interesting than the "innovative countermeasures" prisoners have also reportedly come up with to dodge the devices, though, is the admission that Stringrays are being used in the first place.

While the use of Stringrays by authorities in the US is common knowledge, never before has their deployment in the UK been officially confirmed. It has long been suspected, of course, with plenty of believable if not conclusive evidence they've been used in surveillance for many years. Now we know for sure the SPS has them to hand, you can bet that law enforcement and intelligence agencies are well-acquainted with Stringray technology.