From 1st October 2008 all buildings, whether residential, commercial or industrial, are required to have an Energy Performance Certificate (EPC) for every occasion they are bought, sold or RENTED.
It will be illegal to advertise a property to rent unless it has a valid EPC
which must include cost effective recommendations to improve the
energy performance of the property. The fine for non-compliance will
be £200. Landlords offering property for rent will be required by law
to provide prospective tenants with an Energy Performance Certificate
for their property.

< Example of energy
efficiency rating
certificate for homes
The EPC's will have to be provided free either when (or before) any written information about the property is provided to prospective tenants or a viewing is conducted. They will not have to be provided if the landlord believes the prospective tenant is unlikely to have sufficient funds to rent the property or is not genuinely interested in renting, or the landlord is unlikely to be prepared to rent the property to the prospective tenant.
A new certificate will not be required on each let since, in the case of rental property, EPCs will be valid for 10 years.