If I still lived in the UK, I would absolutely get a permanent a/c system installed in my house. I agree that UK houses aren't designed with a/c being installed in mind, but scientists tell us that the world is not getting any cooler, so I feel that hotter and hotter summers will be the norm. I don't do well in heat so a/c (even in the UK) would be a must for me.
I joke with friends that houses here in the USA are made out of papier-mâché (well, wood). They're not typically built of brick and aren't super well insulated, and are typically only cooled and heated with air (fireplaces notwithstanding). In order to overcome this, houses in my area have large a/c systems and gas-fired furnaces (often multiple of each). Electricity and gas are pretty cheap here so I don't personally worry about the (no doubt massive) cooling and heating inefficiencies. We're currently paying about £0.08 per kWH and £0.34 per therm.
