Yesterday's moneysavingexpert weekly email alerted me to the fact that Sainsburys have an energy supply arm, but it's operated under British Gas - and is cheaper!
So I've spent an hour getting all the details needed and now signed up, with a price promise till next March - and will have saved us £174 for the year
Our usage is quite low, so others should save quite a bit more.
Here's the link if anyone's interested http://www.sainsburysenergy.com/
It was quite easy; I logged onto our British gas a/c and got actual usage figures so I could get an accurate quote, and of course checked how much we'd paid over the last year.
One hour's work, £174 earned