RedTape

DanielDavies has a good analysis of why planning enquiries spiral in scope and cost :

https://backofmind.substack.com/p/slight-return

In short, because of privatisation of so many government functions, the government overseers don't have visibility of the project. Therefore can't make informed TradeOffs about the project.

Therefore any proposed project has to make its own case. And part of that is to avoid stepping on any legal land-mines (where the paper-work is incorrect). Furthermore as in most projects, there are those who support and oppose it. Because it is a legal mine-field, those on the losing side are quick to turn to litigation. Which also means that a large private sector of third-party services companies has grown-up to support such litigation. Which means that it's easier. So projects have to be even more careful ... and round we go.