Stay inside, where it's air conditioned. Outside, it's got to be in the 90s right now, but it's cool enough in the house that I'm wearing a snuggie (don't laugh, it's just a blanket with sleeves -- really useful for surfing the web).
As for what you can do about the heat when you don't have air conditioning, open up some windows and get a cross breeze going. I don't know what the architecture is like in the U.K., but here in the Southern U.S., it's pretty standard procedure to make sure there are at least two windows in every room that shares a wall with the outside of the house, preferable on opposite sides of the house or, failing that, on the next wall over. It allows you to open the windows and get not just a little bit of ventilation, but a full blown breeze going through the house.
Also, I find that stripping down to nothing but a pair of shorts helps a lot. Under the snuggie, I'm wearing a pair of swim trunks and no shirt. It feels good.