From the 1st of October 2008 any property advertised or available for rent will require an Energy performance certificate. We must be able to show a copy of this to any potential tenant and can be fined for not doing so.
I have composed some more information below for you but in a nutshell;-
You can have them done yourself provided you use a qualified person but we can organise them for you and will be charging 70.00 with no v.a.t. as we have sourced an independent local lady.
They will last ten years and you only need them when the house is available for rent again not if the house is occupied currently by a tenant.
Even if the rating comes back as poor you are not enforced to necessarily do anything and personally I doubt most tenants will take much notice.

Further Information.
An EPC (Energy Performance Certificate) gives a rating for your home in its present condition and also a rating for its potential if certain energy saving improvements are undertaken. The overall assessment is based on a sliding scale of A to F, A is the top level (most efficient) and G (least efficient). To simplify the rating scales a similar method to that used for home appliances (e.g. fridges, freezers etc) was adopted.
There are many lots to consider when calculating the ratings for an EPC for every home, as each house is different.
The basic criteria for energy assessment include:
Building Construction
Age of construction
Number of windows and type
Volumetric calculation of all floors
Method of heating and controls used
Levels of insulation (lofts and walls)
Thermal properties of adjacent buildings
Heat losses
Fixed lighting efficiency
Renewable energy sources e.g. solar panels, domestic wind turbines
The factors detailed above are noted, and, using computer software an overall rating can be obtained, together with recommendations for improvement where required.