Now here's a funny thing. I started a fixed price contract with Scottish Power 10/11/11. The contract is called Online Fixed Price Energy December 2012, and the prices are fixed until 30/11/12. At the end of the period, I have the options to move to another Scottish Power product, or to the standard Scottish Power monthly direct debit, or move to another supplier. So six months in, having built up a hefty debit as expected at the end of the Winter period, I get the usual notice that my direct debit is being increased by 60%; no explanation was given, although Ofgem say that the supplier should clearly explain how the increase was calculated. When I queried the increase, I was told the increase was based on a year's estimated usage, ie to April 2013, plus paying off the debit which had accumulated over the last six months. My belief is that since I am on a fixed price, fixed term tariff, Scottish Power can only base my direct debit amount on my account balance and estimated consumption up to the end of the fixed term. Ofgem publish advice on direct debit practices for the Big Six suppliers, effective as at November 2011. This shows that Scottish Power accounts should balance on the anniversary of the start date of the contract. I will start the formal complaint process with Scottish Power immediately, however if anyone has any comments, I would be glad to see them. Thanks for your help!