It's not a dumpster it's a skip they're different things.

A dumpster is basically something you put trash in. A skip is what you put building waste in (rubble, bits of drywall), so firstly it's larger than you're thinking, if you're thinking of a dumpster. Seriously if you get in one it's kind of hard to get back out again without somebody helping you, they go at least five foot up. Secondly he's doing this to prove a point, and the point he's trying to prove is that he's a belligerent idiot, and he's proving it very well. It's not that homes in London are expensive, although they are, his "problem" is that what he wants to do isn't legal (he wants to live in a caravan on that plot of land and it isn't zoned for that), so he's doing this instead as a loophole. It isn't some protest against home prices in London or anything noble like that.

However the media lap it up and he's quite happy to make use of it to further his cause of being an annoying pain.