drypin saidI believe you meant his castle is not his home.
That's what the article read, but the old saying is that a man's home is his castle, meaning it cannot be invaded illegally by the state (except in the US during the Bush Administration).
The problem here is that he built this castle/home illegally in the first place, and kept it camouflaged from the authorities. He claims a technical legal point in British law that he's occupied it for over 4 years now, which may protect him from the consequences of his have violated building codes.
A strange legal quagmire, and it makes you wonder why he took this deliberate course of action in the first place, knowing it was fundamentally illegal when he started.