Customers of some energy suppliers will be asked to reduce their electricity consumption this evening in a bid to halt blackouts around the country.
As the UK suffers freezing temperatures and snow in many areas, there has been an increase in demand for power at a time when supplies are tight.
The National Grid triggered its back-up power plan amid fears energy supplies could run out, causing blackouts.
It has given notice to two of its reserve coal-fired power stations to fire up and be ready to produce energy if called on by the grid.
The network's operator said the emergency plan "should give the public confidence in Monday's energy supply", with travel disruptions meaning millions are expected to work from home and turn up the heating.
UK next-day electricity prices surged yesterday to help attract power imports through interconnectors from Europe and record prices are expected during the peak demand hours on Monday.
For this reason, some people are being asked to cut down on their electricity use between 5pm and 7pm today.
National Grid says that the service is just a test and had already been planned for today, however, the timing will likely still be useful on a day when energy prices have shot up.
Octopus Energy has promised that its customers can save more electricity than other suppliers, with Drax and Eon also saying they can provide significant savings for the grid.
The grid had prepared two Drax stations in North Yorkshire for use this evening, which are among five put on standby under so-called winter contingency contracts, with others run by EDF and Uniper.
The two units are each said to be capable of generating around 570 megawatts - adding more than 1.1 gigawatts to the grid if used.
A spokesperson for the National Grid said: "We've issued a notification to warm two winter contingency coal units. This measure should give the public confidence in Monday’s energy supply."
The warning, they said, was just a contingency plan, and would only happen "if required".
"The ESO as a prudent system operator has these tools for additional contingency to operate the network as normal and the public should continue to use energy as normal," the spokesperson added.
