He's deliberately built it in a skip because that's the loop-hole. Houses come with all kinds of regs/costs involved - these costs are magnified in London.

There's literally no way you could legally build a house on the land for anything remotely close to that - maybe even at all.

Conversely, you're allowed to put whatever you want in a skip, as long as it fits. And you can put a skip pretty much anywhere on your own property.

The obvious downside is that his house doesn't technically exist. However, the upside is that his house doesn't technically exist also.