The National Grid has triggered its back-up power plan amid fears energy suppliers could run out, causing blackouts.
As temperatures drop below zero and swathes of the country is covered in snow, the network is facing a surge in demand.
National Grid has subsequently 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.
The triggering of the plan did not mean that the coal-fired units will be used on Monday, but that they will be available to the grid, if required, said the National Grid Electricity System Operator.
"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," it said.
It comes as parts of the UK wake up to several inches of snow this morning as the current cold snap continues into this week, with temperatures plunging as low as -10C.
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.
The UK faces its biggest test yet with the current cold snap – which has seen the country suffer freezing temperatures and snow in many areas – ramping up demand for power at a time when supplies are tight.
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 between 5pm and 7pm on Monday.
The instruction for the coal-fired plants marks the first since they were put on standby and comes as the grid said it will also run another test of its demand flexibility service – which pays customers to use less electricity during certain hours.
On Monday, customers of some energy suppliers will be asked to reduce their consumption between 5pm and 7pm this evening.
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 expects that the coal-fired stations will be ready for use if called upon for the evening between 5pm and 9pm, when demand is set to peak.
The stations are operated by Drax in North Yorkshire and are two of 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.
