In reply to Heike:
As has been alluded to above, ae you talking the utility company's guesstimate, or your actual measured consumption?
If the former: take a reading, now. Then repeat this every week for the next four weeks. By the end of this you will have a very good idea of how much energy you are actually using. Then you can times this by the unit price, add the standing charge, and work out what your true monthly cost is. If you've been allowing them to estimate it then I bet it'll be somewhat lower... (of course you need to allow for increased costs over the winter).
If for whatever reason you can't do this then get smart meters straight away and let it do the work for you.
I am eternally astonished by people who measure their energy consumption in £, and who allow estimated readings to drift for months and months, as if they think that the estimate is somehow an 'all-you-can-eat' tariff.
Dax - sorry if the above sounds harsh! You are, however, protected by back-billing rules and they can't charge you for anything used (and not billed for) from more than 12 months ago. If you feel you should pay it regardless then that's your call...