Energy Performance Certificates illustrate the energy efficiency of homes on a scale from A to G. Those in Band A are the most efficient, and will usually have the lowest fuel bills.
The same scale is used to define the impact of a property on the environment. Higher rated homes will usually have less impact through carbon dioxide (CO2) emissions.
To put this into perspective, the average property in the UK is in band D or E for both ratings.
The Certificate also makes energy saving recommendations that may help reduce future energy bills. In some cases, these can be financed under the Government's Green Deal. In effect, Green Deal offers UK home-owners a loan, which is repaid through regular electricity bills. The main loan condition (the "Golden Rule") is that the amount saved each year on energy bills should be more than the cost of annual loan repayments. Note that the loan stays with the house when owners move on.