Re: "an alert would be sent to security staff who could then confront the suspected thief"
>I'm sorry but that does not chime with legal rights. I will admit you have the right to watch me, but if you come up to me and ask me to leave the shop I'm going to demand what right you have to do so...
Simple -- see notice posted prominently near the entrance "We reserve the right to refuse service to anyone". You British have really got to get a handle on this rights thing, its like the concept was imported some years ago without really being understood. So when the police turn up -- if they turn up -- they're not going to be very happy with you because you're causing a disturbance and, believe it or not, you're trespassing (as the store owner or his/her representative has asked you to leave).
Its really not a color thing, either. This technology is in wide use in Las Vegas, its how card sharps and pickpockets are identified. Video surveillance is ubiqutous and if there's any suspicion of someone playing against the rules they'll be watched carefully and if they are found to be cheating they'll be pulled aside, there will be a quiet talk in an office, they'll be photographed and what-have-you and sent on their way. From that moment on any attempt to enter any casino will be flagged. Its not unreasonable to get the same treatment from a store; you will be watched -- there's typically a prominent notice and a screen showing you video surveillance at work -- and they'll zero in on anyone who looks suspicious. (Its actually a little trick I used to get the attention of an employee at a big box store such as Home Depot -- if you look a bit furtive then sooner rather than later a friendly employee will turn up and ask you if you need anything. Works a treat.)
(I suspect that the reason why there's all this fuss is that the era of the 'five fingered discount' is drawing to a close.)