After much prevarication my house now uses 100% renewable electricity, with Ecotricity as my new supplier.
Add to this the carbon offset for motoring, which I started in 2006 and my offset for air travel, which I started in January and I am slowly reducing my carbon footprint. For these two, of course, an offset is a very poor substitute for not generating the carbon in the first place, but right now I can't reduce my road miles and am not willing to reduce my air miles. Offset is a reasonable second best.
My next mission is to get my place of work on renewable electricity.