Britain’s power system operator has triggered contingency plans in case supplies can’t keep up with demand in the current cold snap.

National Grid ESO issued a so-called electricity margin notice (EMN) overnight and later ordered four out of five coal-fired plants, kept in reserve, to warm up in case they were needed.

It said of the EMN: “This is a routine tool that we use most winters, and means we are asking generators to make available any additional generation capacity they may have,” the company said on Twitter.

An EMN does not mean electricity supply was at risk, it added.

Separately, start-up instructions were issued to generators – two at Drax’s site in North Yorkshire and two at West Burton in Lincolnshire.

While they will not necessarily be needed, they will be available if required.

National Grid ESO said the EMN was in place for the hours between 4.30pm and 8.30pm on Tuesday.

The notice reflects efforts to ensure the lights can be kept on as the northern half of Britain, in particular, is hit by snow and ice.

Temperatures overnight are forecast to fall as low as -15C in some areas of Scotland.

UK weather – latest: Forecasts warn of -15C as snow and ice to hit roads, trains and bus services

The power grid operator has used other tools in its box during the winter to help protect supply margins, such as triggering the Demand Flexibility Service, which sees household signatories paid to turn off high-usage appliances at peak times.

The UK has five coal-fired units that are ready to be switched on if required to help guarantee energy security.

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They have become increasingly important in the wake of Russia’s war in Ukraine which disrupted gas supplies to Europe and when the wind hasn’t blown.

While the UK shares power through so-called interconnectors with other countries, the gas squeeze has combined with other factors to damage the ability to import electricity when needed.

These have included a large number of nuclear plant shutdowns in France, though capacity has improved as the winter months have progressed.

A relatively mild winter on the continent has also prevented countries from burning through their gas stocks.

An ESO spokesperson added: “The ESO has issued a notification that we will warm four of our five winter contingency coal units for potential use on Tuesday 7 March.

“This notification is not confirmation that the unit will be used on Tuesday, but that it will be available to the ESO, if required.

“The ESO as a prudent system operator has developed these tools for additional contingency to operate the network as normal. This does not mean electricity supplies are at risk.”