These "home pong" consoles were very common at the time. They don't really do much, so their main value is historical interest, and this isn't a particularly famous model. A quick eBay search seems to indicate it might go for GBP 80 at most, but probably more like GBP 20-40. So OP got a good deal, but they didn't find a lost Vermeer. :)

Nah, it's a cheap pong clone, it doesn't have that much collector's value. Also I can just pack everything back up, it wasn't sealed just wrapped in plastic.