I recently changed my electricity supplier after doing a comparison on the uSwitch web site.
But who are the electricity end user suppliers getting their electricity from? Well they are buying from the generators who are creating that power by various methods, some more environmentally friendly than others.
Different suppliers buy from different mixes of sources and over at ElectricityInfo.org they give breakdowns for all the companies.
For example Good Energy are listed as having got 100% of their electricity from renewable sources in the year 1 April 2012 to 31 March 2013. By contrast 73.7% of EDF Energy electricity came from nuclear power plants during the same period.