Rich
look at it this way, by keeping the 'control' that you think you have you are only really keeping hundred quid per year at best (fluctuating between summer and winter) in your own account earning at best 1% interest. if you pay for your energy by DD, you immediately save yourself about 6% off your bill !!!!!
If you really want to decrease your energy bills, pay by DD, go to an online tariff with paperless bills and take elec and gas from the same supplier. (and ensure to give meter readings)
and support the UK economy by going with BRITISH Gas