It's sad, but Maplin as a proper component store died in the 1990s. I remember going into the Sheffield branch in the early noughties wanting a couple of bipolar transistors (I wasn't particularly fussed about what, as long as it could sink a few tens of milliamps). With some help from the guy on the
component LEDs and speaker cable counter we eventually found one that was in stock. There were another 3 in the Liverpool branch, apparently. Should have gone to Bardwells
[1] I know, but that was the other side of town.
They've continued to be useful for things like wall-warts, A/V cables and connectors, and distress purchases of computer parts, but you can't run a highstreet chain on that. I suspect the DJ tat
[2] and electronic toys market has now been displaced by online sales to the point where it just wasn't viable. Pretty much the same thing that happened to Tandy, but in slow motion. (I got some lovely bargains from a Tandy store in 1998 as it sold off a load of electronics and audio gear in a last-ditch attempt to re-invent itself as a mobile phone shop.
It's pleasing that the Maker movement has re-kindled hobby electronics, and there seem to be plenty of online businesses (as they pragmatically have to be) selling kits and components to that market - some of which aren't even based in Shenzhen. And if your needs are more specialised the industrial suppliers (Farnell/CPC, RS, Rapid, etc) haven't gone away. But you can forget about wandering into a high-street shop for a roll of solder and some headphone plugs.
[1] Arse. They closed last year. That really was an institution.
[2] Proper lighting and sound equipment has always been the domain of quirky businesses on industrial estates.