Hello Matt I feel I have to answer you I also live in the uk and I have experenced the same thing with my boy I tried everything I thought, even had him castrated, but he was still the same then another breeder suggested I get his thyroid checked at first the test came back normal but they did say the lab had said there was a more intensive test so I had that done -result low thyroid he is now on 1 tablet a day and what a difference he has gone back to be a very loving boy no more problems I noticed in dec he started bein a bit funny again retested and he just needed his dose up a little since then no problems at all just a beautiful boy
The potential is very exciting. Unfortunately not everyone considers the bloodlines and illness/disease when deciding to breed. I feel very strongly about this issue as I own a basenji who has suffered all her life with an ulcerated throat/stomach. I only hope in future people will be more responsible.