+1 on the solar panel and a/c suggestion.

If you can't afford to install central a/c. A portable unit will set you back £300 odd at Argos, and easily cool a room down (like an art studio, for example). just make sure it has a compressor or lists BTU measurements... otherwise it's probably a water cooler in a trench coat, rather than true Aircon, and the British climate doesnt allow water coolers to work all that effectively.

I recommend them to lots of people who rent or can't afford the renovation costs associated with A/C etc, and most are more than happy with results