Three UK coal plants have been ordered to begin warming up in case they are needed for the country’s energy supply as the cold snap bites.

National Grid ESO said it had given the instructions in light of forecasts showing electricity supply margins may be tighter than normal on Monday.

It added it was also activating a live “demand flexibility service” – which allows the ESO to access additional flexibility when national demand is at its highest during peak winter days – between 5-6pm on Monday.

The scheme entitles some households with smart meters to discounts if they cut their use of electricity.

It is due to stay in place until March, with 26 energy suppliers including Octopus Energy and EDF signed up to it, but until now has only been used in tests.

National Grid ESO added that its announcement should not be interpreted as a sign that electricity supplies are at risk and said “people should not be worried”.

“These are precautionary measures to maintain the buffer of spare capacity we need,” National Grid said in a tweet.

The cold weather means more people are heating their homes which increases demand for energy, but a lack of wind has reduced the amount of renewable energy available.