Tech9
Part of the Furniture
but there seems to be a real loss of Speed and quite possibly Interference
I would say find how to disable Wi-Fi on BT device, because you're in UK and only Ch.42 (36-48 @80MHz) may be available to you in non-DFS range. There is a chance both your routers fight for the same channels. Here in North America is different - I can have 2 routers side by side working on Ch.42 and Ch.155 (149-161 @80MHz) and set on Auto. Your situation is a bit region specific and I know it because I have a place in Europe too.