In the original bunker video, he applied for planning permission /after/ it was built https://planning.southkesteven.gov.uk/SKDC/S16-0017/1288446....

It's also quite funny he names "Mr Malcolm" as the person who gave him advice before hand. He's also been arrested for other projects.

I feel like he's very much "do first, ask later" type of person. And at least with both of these projects they're sponsored. So it's not costing him anything.