UK and EASA regulation implemntation

Not directly related to Ardupilot but I know there are a lot of commercial operators based in the UK that frequent these forums.

I am getting my head around the changes but am coming up blank when it comes to aircraft classification within the open and specific categories.

The general documentation only ever refers to “off the shelf” UAVs. Nowhere can I find details on how one operates a self built platform in the new regulatory framework. Have I missed something really obvious somewhere?

The documents I can find talk about the design and acceptance standards for manufacturers of UAS but the process of compliance is not clear and would be enormously burdensome if each UAV built is a “one off” intended for internal use not for sale.