Is it against the law to build a home for your family - no. Where else can they go?
Building a house is not inherently against the law, but there are myriads of ways in which you can break the law in the process - off the top of my head, you could fraudulently obtain the goods and services to build it with, build it not in accordance with planning permissions, or in contravention of building regulations, you could commit health and safety breaches in the course of building it, destroy wildlife or flora in contravention of various Acts of Parliament.
The other side of the coin, do we really need to send someone like that to prison, which will cost the state more.
Leaving aside the question of whether costing the state is the most important criterion in deciding what to do, what
do we do with someone who has, from the sound of it, quite deliberately set out to flout the planning rules, and appears to be unrepentant - given that the row is still going on 9 years later - about remedying that?
If he's allowed to just keep his eyesore with no penalty, he sets a precedent for simply disregarding planning regulations - which are, at least potentially, there for very good reasons - which could result in people all over the country deciding that they, too, can choose to get away with disregarding the rules. Again, it might be hard to put a price on that, but do we want to live in a country where people can jerrybuild mock tudor "castles" anywhere they feel like it?