And I was grateful that over on twitter pozorvlak asked how reliable those figures were. Because we both got a reply shortly thereafter from chasbooth with two links. Which allow you to see that energy costs are about 14% higher for electricity and 3% higher for gas.
Articles here and here (page 221 of the latter).
Those costs are from 2008, and will be higher now (as the renewables obligation rises over time to foster more carbon-free resource generation), but it's nice to at least have some actual figures.
Original post on Dreamwidth - there are comments there.