DECC does not hold any data on electricity and gas bills on a monthly basis or by property size.
The Department’s latest estimates for the average annual domestic energy bills relate to the year to December 2008 and are published in Quarterly Energy Prices, the latest edition of which was published in March 2009, available online at:
http://www.berr.gov.uk/energy/statistics/publications/prices/index.html/statistics/publications/prices/index.html
For an average consumer using 3,300 kWh of electricity and 18,000 kWh of gas per year and paying their bills on receipt (standard credit), in 2008 the average annual electricity bill was £405 and the average gas bill was £570.