I think what you're really seeing is a stark contrast between "haves" and "have nots".
I live in a city, but my parents still live in the town where I grew up, which has its nicer and not-so-nice areas - in the area my parents are, you can't move for bumping into high-end cars and designer labels. I'm talking cars which cost the equivalent of the NMW each year to run/service even without the petrol. You wouldn't think we were in a recession if you only look in that area - not at all. It's hard to generalise but most of the folks there are mid-age/older, typically bought/owned their homes before the boom years (i.e. 10+ years ago), fairly professional jobs, etc.
And yet walk 30 minutes down the main road, you're into the council housing estates where you're lucky if the average household income will be half the country average.
There's a real difference between those households, and yet if you walk into the town shopping centre it's crammed with shoppers doing just as you described.
There is plenty of money around, trust me, but amongst those crowds are the ones that can't really afford it who are mixed in too. And you're mistaking them all for the folks who really do have the disposable cash to shop like that.
A good example of this is I have a neighbour who I occasionally take in parcels for - she's very friendly but is one of those "only brands will do for my children" types. Which is great if you can afford it, but she works in Iceland, on the till, so I'm guessing at or just above NMW. How can a single mum like that afford to spend £60 on a pair of toddler shoes? (one example from last week) Either she's rolling in cash (I don't think so) or she's living beyond her means really.
Because there really is a crowd of people in the UK who can afford a lot of the luxury goods being sold, but there's even more who think they can afford it, but really can't.
Maybe i'm explaining myself badly here, but I think the crux of it is that the average Briton considers themselves far richer than they really are - many of us are living beyond our means, be that by buying brands regularly that our income levels couldn't possibly sustain, or by avoiding paying into pensions, for example, which is another ticking timebomb our generation is going to be facing in 30, 40 years time.
The booming shopping centres aren't necessarily something to be celebrated if we scratch beneath the surface - the growing income equality in this country hasn't had the airtime it really deserves.