Good point Shopps - I'd not taken that into account.
It's dispiriting if the people that can do something are too apathetic to do anything, and the people that would do something would have to break the law to do so, so can't! Sounds like a bit of a catch 22.
I suppose you could film yourself making a loud running commentary - for example: "I'm in XXX store in XXX town on XXX day and time, and I've just been targeted by a gang of X number of young girls/lads, first they did X, and now they have done Y, all the while the shop staff and security are doing nothing to help...".
Of course the store could then hide behind a "no filming in store" policy, but probably not before you could get it out there to embarrass their PR department!
Society seems to have evolved in 2 opposite directions at the same time - behaviour is getting worse, and the ability and will to do anything about it has diminished.
Once upon a time when you were growing up, you would get pulled up for your behaviour by your neighbours and your friends' parents, and the teachers from your school. Some cultures still have this idea that not only the parents but the wider community are involved in the raising of a child (eg: an African proverb - it takes a village to raise a child), but it's clearly dying out in the UK.