Bob at work pointed out an article in the Ends Report that suggests British Gas's Zero Carbon electricity tariff is greener than my Good Energy tariff. I wrote the following to Good Energy:

I read in the August 2007 Ends Report that British Gas retires 12% of ROCs above its legal obligation for its Zero Carbon tariff, whereas Good Energy only retires 5% above its obligation. I'm a very happy customer of Good Energy, but I'm tempted by the Zero Carbon tariff. Is there a reason why I shouldn't switch to British Gas?