There are no punishments. Most crime is effectively decriminalised because the police don't have the time or resources to investigate so these people know they can get away with whatever they want. A lot of shops have cut back on security to save money. Places like Home Bargains have a picture of a security guard. They rely on staff being present to be enough of a deterrent but it isn't and even if caught by those staff they will just walk away because the staff aren't going to risk being attacked to save a business a few quid when they are only being paid minimum wage. It's not just shoplifting either. Burglary, car theft etc is rife for the same lack of police resource issue.
I was in a queue at lunchtime in Greggs a few weeks back. Long queue at a busy time of day and a bloke walked in, said excuse me to get to the sandwiches, grabbed a few and then just walked out. When I got out he and another homeless person were just sitting outside eating them. Didn't even bother trying to hide or be discreet about it.