Defra - the goverment department for Environment, Food and Rural Affairs. Here you can find information about energy efficency, combined heat and power, and fuel poverty.
CLG - the Government Department for Communities and Local Government. Formerly the Office of the Deputy Prime Minister. Contains information on Building Regulations, including Part L.
Energy Performance Certificates - Directgov is the website of the UK government providing information and online services for the public.
EST - the Energy Saving Trust. EST encourage energy efficiency and the adoption of renewable energy sources.
SAP Boiler Efficiency database - used in ecmk Software.
The Carbon Trust - whose mission is to accelerate the move to a low carbon economy by working with organisations to reduce carbon emissions and develop commercial low carbon technologies.