stressed1,
The first point to make is that an energy supplier should, by law, only charge you for the past one years worth of energy if they have failed to bill you correctly.
If you have been paying by MDD then you need to speak to the supplier to see how this bill has been produced and where the money has gone you've been paying over the past 2-years.
In terms of average energy bills, the average consumption in the UK is 20,500kwh gas and 3,300kwh electric per annum. Using current energy prices, this puts the average energy bill (standard tariff) at £1,350.
Hope this helps.
Regards,
Scott Byrom
Utilities Manager
moneysupermarket.com