In my experience the only way to make a builder sit up and take notice is to keep a tight hold of the retention monies until the defects and snags and complete. To my satisfaction.
Even then sometimes it's not enough. Don't ask how I know 🙈
MPJ and Coalhill are the same. I thought I had stopped using my MPJ account as I was unable to log in to the forum on my phone / new laptop. But it seems my old computer was still logged in as MPJ. Sorry for the confusion and mystery. Yes, Amersham was lovely, I lived there for 59 years, but have now moved to Yorkshire, and have a small holiday flat in Leeds!