I lived for a few years living around the New Cross/Bermondsey area (south of the river, but similar in demographic to the areas in TFA) and there were always a few electronics shops whose existence seemed fundamentally implausible if their business was founded on anything other than handling stolen goods. I avoided them like the plague, but they were generally pretty resilient businesses - and if one closed down, another would spring up a few streets away. I'm not saying that any business which looks a bit grungy is dishonest. I've made some good purchases at backstreet computer stores which get good prices on the back of low overheads and connections with legitimate suppliers (though such places are rare these days since the online boom). But there's a certain type of business which is offering games consoles or other commodity goods at the kind of prices that just make you go "hmm".
Hell, even going back well before that, I can remember independent video games stores "Ooop North" (from the tail end of the period before the big chains drove most of them to the wall, around the early PS1/N64 era) who were well known among my teenaged peers for staying in business on the basis of a combination of modchipping and fencing stolen goods. In fact, I remember one very close to my school being raided by police and shut down (presumably after crossing some nebulous line into their visible spectrum). Provided a fascinating distraction during the middle of an otherwise dull day at school.
As the whole modchipping thing implies, these have never been businesses run by people without a degree of tech-savvy. It's no surprise that they've moved onto circumventing mobile phone protections. And I bet you'd find similar businesses in, at the very least, Manchester, Birmingham, Liverpool, Newcastle and Glasgow.
There have even been suggestions - though I offer no comment as to their veracity - that a well-known red-logoed chain of second hand electronics stores with a presence in almost every town in the UK might sometimes be less than choosy about checking the provenance of the goods it accepts.