What is the National Grid?
The National Grid owns and operates the enormous system of pipes that transports gas around Britain, known as the National Transmission Systems.
The £13.8 billion ($19.1 billion) network comprises over 4,400 miles (7,000 km) of high-pressure pipe and more than 600 above-ground installations.
Its job is to balance supply and demand of gas across the country, but does not sell the fuel itself.
Instead, the gas is sold to home and business owners by supplier such as British Gas, NPower and EDF energy.
Is it possible to run out of gas?
The UK's gas reserves are filled by its power stations as well as import pipelines from Norway, the Netherlands and Belgium.
To run out of gas, Britain simply has to cross the so-called 'margin' - the difference between peak demand and available supply from these sources.
If it gets too low, National Grid can issue warnings to generators to begin producing