Since 1 October 2008, landords of self-contained, privately rented properties have have been required to provide an Energy Performance Certificate (EPC) to new tenants. An EPC gives information on the energy efficiency of the property and allows prospective tenants to compare the energy efficiency of different properties, and gives an indication of the possible running costs.
For further information about EPCs use this link.
http://epc.direct.gov.uk/index.html