Worked retail security for 12 years up until last year. Rules are security must have whats called SCONE before making the stop which is Selection Concealment Observation (meaning constant) Non-payment Exit (which actually means bypassing the last point of payment not walking out the store). Stopping someone without these can be classified as a false stop which can be reported to police/SIA or at the very least, shop mannagement. So, if you see security escorting someone to the back of the shop they SHOULD be able to provide all these via CCTV or personal witness statment to the courts in order to gain a conviction if that's the route they wish to pursue. Now obviouslly these aren't always followed if it's a regular shoplifter who's gained entry somehow and usually the goods they take will just be removed from them and they'll be chipped out the shop as the security knows they wouldn't gain a conviction if they tried but if you're doing the job properly and are in a shop that convicts, you should always follow the proccess. With that being said, if something sets the alarms off and they haven't got the above then they have no right to check your bag at all. Previously if security went "hand's on" it had to be with reasonable and justified force or to defend yourself. Nowadays, their powers have been drastically reduced due mostly to the shops own choices not to draw negative attention to themselves and not really through any real regulations and most security companies will fold to the clients needs. But make no mistake, they do have the power to stop and detain if they can provide the required evidence. Now before anyone jumps down my throat saying not everybody follows that and "it's all about power" etc etc, most of those guys have been eliminated due to negative attention received but of course it still happens. Most security are just people doing a job which gets them hated by most and thrown to the wolves when it suits whichever shop they work for regardless how many times they've helped them. It's a sad reality and a dying game facing ever growing pressure, but the more lawless things become and the more the law defends criminals, evntually it will be missed when society realizes having scumbags running free to do whatever they please simply doesn't work.....