Hi Blue Sea,
Sorry to hear about your dad's problems. When my mom was first started on Seroquel, at a low dose (sorry, I don't remember specifics), it was like a miracle drug. Big improvement in behavior with no ill effects. But, as with your dad, after several months of continued progression of her dementia, the aggression started up again. At that point, after several short hospitalizations, many changes of medication, and general consternation, we moved her from an assisted living facility (not equipped to handle dementia) to the dementia home where she now is.
When the assisted living place told us my mom could no longer stay there, they recommended Silverado (where she now is): they take the tough cases. I was apprehensive about this, as I envisioned something pretty institutional (like the mental hospital wards where my mom stayed briefly). I was very pleasantly surprised at what Silverado actually is -- anything but institutional! They are very good at compassionately and respectfully dealing with folks with dementia, and it is a very residential atmosphere. Anyway, the point is a place doesn't have to be bad in order to handle "challenging behavior."
I'm not in the U.K. , so don't know exactly what "EMI" is or what types of homes there are there. I hope if you need to find a new place you'll find one you are comfortable with.
Karen