The large energy suppliers (often also called the 'Big Six') are the companies that hold supply licences and supply most of the energy to domestic households in the GB market. They are:
Centrica plc (parent company of British Gas), E.ON UK, Scottish and Southern Energy (SSE), RWE npower, EDF Energy and ScottishPower.
All energy companies must operate under a licence condition (or exemption/exception) if they supply gas and/or electricity services. These are administered by Ofgem and relate to the Gas Act 1986 and Electricity Act 1989.
A consumer who annually uses 2.100 kWh of electricity and/or 11.000 kWh of gas.
A discount that is paid at a pre-specified point in time if the consumer does not switch energy suppliers.