I don't think the is anything like that this side of the pond, hell, I don't think I have ever seen a surplus electronics store here at all.
A simple google search of "surplus electronics britain" found these:
http://www.surplus-electronics.co.uk/
http://www.distel.co.uk/
Deeper searching would probably uncover more. Believe me, they are there if you know how and where to look; now, I can't say whether either of the above have an open store front for the public to wander in or not (they may both just be web presences) - give them a call and find out!
Typically, these kinds of places (the real grungy and cool ones, ya know) are going to be in areas where you might say to yourself "self, perhaps I shouldn't park my car here at night" (or sometimes the day!). You know, the areas where there are poor people, junkies, bums, etc (ie, people who may roll you). A lot of times, even immigrant communities. Basically, these places are either forced by one reason or another to locate in areas where the citizens of that area won't make a stink about it to their local government representatives because they can't (maybe they aren't legal residents?) or they have other issues (crime, poverty, etc), or they just don't care.
Sad - but the truth. So, you need to be looking in those areas when you do your research. These places also tend to be home to a lot of other similar business (anything involving steel and dirt - autobody shops, welding shops, scrap metal shops, junkyards, etc). I know you guys have those places (Scrapheap Challenge, anyone?)...
