Infographic: Energy security

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Behind the numbers

You can find fuller historical data and information on how Britain’s energy market is structured, larger supplier prices and profits, energy bills and customer switching via the following links:

Terms explained

Who are the larger energy suppliers?open key term pop-up |  Dual Fuel (DF)open key term pop-upWholesale costsopen key term pop-upNetwork costsopen key term pop-upSupplier operating costsopen key term pop-upEnvironmental and social costsopen key term pop-upPre-tax marginopen key term pop-upSwitchingopen key term pop-up

Who are the larger energy suppliers?

The “Big Six” is the name sometimes collectively given to the six larger energy companies who supply most of Britain’s gas and electricity. Each of them generate electricity, and deliver both gas and electricity to our homes and businesses. They are:

– Centrica plc (three retail brands: British Gas, Scottish Gas and Nwy Prydain in England, Scotland and Wales respectively)
– Scottish and Southern Energy (SSE)
– RWE npower
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Dual Fuel (DF)

A type of energy contract where a customer takes gas and electricity from the same supplier (or two affiliated suppliers).

Wholesale costs

This is the amount energy companies pay to buy gas and electricity which they then sell to you. They may buy from the wholesale market, have a contract with an electricity generator, or be part of a company generating its own energy. Wholesale gas is often bought in advance. If suppliers don’t buy enough, they may have to buy more which can be at a higher price depending on the market.

Network costs

These include the costs to build, maintain and operate the gas pipes and electricity wires run by the network companies who transport energy to your property. 

Suppliers are charged by network companies for this, and pass on this cost to their customers. We limit network costs carefully though price controls. This is because you can’t normally choose which network company you use. You can find out more at more

Supplier operating costs

These are the costs associated with running a retail energy business, including sales, metering and billing.

Environmental and social costs

These are the costs of government programmes to save energy, reduce emissions and encourage take up of renewable energy. They also include the cost of social programmes like the Warm Homes Discount.

Find out more about these at Environmental programmes

Pre-tax margin

This is the difference between the money an energy company receives from their customers and the costs they have to deliver that energy. The ‘margin’ is not just the profit energy companies make. This is because they must pay tax and fund debt payments plus other obligated costs from this money. 


The process of changing gas or electricity supplier, or changing to a new tariff with the same supplier.