How hot is too hot in the UK?

Basically, if it gets to 20°, it’s too hot for me. I can deal with it if I’m in a vest and shorts and there’s a cool breeze. Mid-20s and I’m audibly cursing the meteorological system for turning me into a walking fog bank of sweat and irritability. 30s? Please end me. I’m one of those people who “runs hot.” It takes a cold, cold day before I’m in need of a hoody or jacket, and I can comfortably walk around in shorts and a vest at about 15° or above. When I used to have air conditioning at work, it wouldn’t be unusual for me to have it switched on very early in spring and late into autumn. (I put some of this down to having grown up fat; but then I lost loads of weight, and have recently put some back on, but my temperature tolerance hasn’t really changed at any point). That said, 30°+ in a dry country (I’ve experienced it in the Canary Islands, Greek Islands, Italy) and I’m okay as long as there’s a bit of shade. If air con was widespread in the UK, summers like this would be manageable. I’d like to see it made more commonplace, but then there’s a whole eco issue there that gets exacerbated. No way to win really.