Im not quite sure what you mean. In the UK system everyone is a political appointee. Just how blatent a PM is about interfering in "independent" agencies depends on the PM. And Boris literally just sacked the head of the standards commission and dissolved it to save a political nobody who isn't even needed to shore up a majority.
There is no separation of powers here, as long as the PM is the PM, he is basically god.
There is no separation of powers here, as long as the PM is the PM, he is basically god.