Tip for people trying to stay cool without AC in the UK

Get in the shower and remove the shower head. Run cold water over your femoral arteries (upper inside of your thighs) for 10-15 minutes until you are on the verge of shivering.

This is highly effective as the femoral artery is a major blood vessel and running icy cold water over an extremity is a lot less unpleasant than running it over your core.

edit: I refer specifically to the UK as it is particularly hot here at the moment, but obviously this applies anywhere where most people don't have AC