People will be paid to use less electricity on Monday
Up to a million households in England, Scotland, and Wales will be paid to use less electricity on Monday evening as part of a scheme to avoid blackouts.
National Grid said its Demand Flexibility Service, which has only been used in tests so far, would run between 17:00 and 18:00 GMT.
Those who have signed up will get discounts on their bills if they do things like delay using their oven.
The cold snap has seen energy use rise as more people turn on the heating.
National Grid will decide this afternoon whether it will need to run the scheme again tomorrow.
People struggling could get lower energy prices
The grid operator had also asked for three coal-fired generators to be put on standby in case electricity supplies ran low, but it has now stood them down.
Could you get money off your bill?
According to National Grid, the first thing you should do is check whether your supplier is one of the 26 that has signed up to the scheme. You'll get a notification that it starts today.
People in England, Scotland, and Wales who have a smart meter are eligible.
Customers will receive a discount if they reduce their electricity use between the times set by National Grid. On Monday the scheme will run between 17:00 and 18:00 GMT.
You can save by doing things like delaying using your washing machine or tumble dryer, or charging your electric vehicle.
National Grid says savings can range from a few pounds to as much as £20 depending on the amount of energy used.
This week's cold snap is expected to lead to high power demand, while wind power is forecast to be lower than usual.
It is also uncertain whether the UK will be able to import the power it needs via undersea cables from Europe.
To try to reduce demand, National Grid has activated its Demand Flexibility Service.
But the scheme is only available to homes with smart meters, and the BBC has been contacted by several people who are frustrated that they cannot participate due to not having a smart meter.(Have they bollocks - this is more psycho-mind f**king)
Tonight will be the second time mum-of-three Sarah Chambers, 51, from Wales takes part in the energy-saving scheme with her supplier Octopus.
The last time was during a test in October when she saved about £5 in a one-hour session.
She told the BBC she was “excited” about taking part on Monday and had even pre-charged smartphones and laptops for the family to watch TV and play games on.
“I won't be running the tumble dryer or the washing machine as I usually do when the children come home with dirty PE kits after school,” she added.
“The dishwasher won't be running either as I won't be cooking tea - so no oven either.”
'Consumers are engaged'
[So no hot meals and no washing - hungry kids watching TV on mobile phones - is it really worth a fiver?]
According to National Grid's electricity system operator, more than a million households and businesses have now signed up to take part.
The scheme was introduced last year and is scheduled to run until March.
There were initially concerns it would not attract enough interest due to the level of discounts being offered. But Craig Dyke, head of national control at National Grid ESO, told the BBC that during the nine tests so far, consumers had saved more energy than forecast.
“To us, that tells us that the consumers are engaged,” he said.
On Sunday, National Grid ordered three UK coal plants to begin warming up in case they were needed to generate electricity on Monday.
Power station operator Drax was asked to prepare two coal-fired units and EDF was warming up its West Burton plant.
National Grid - which has now stood the plants down - had said “people should not be worried” by the move and electricity supplies were not at risk.
A similar request to warm up coal plants was made in December last year, although in the event they were not used.
Last summer, the UK government asked Drax to extend the life of its coal-fired generators due to fears over the security of energy supplies following Russia's invasion of Ukraine.
The Drax plants had been due to close in September, but the company agreed to keep them online until March 2023.
National Grid's boss told the BBC last year that blackouts would be a last resort this winter if energy supplies run low.
John Pettigrew said National Grid's “base case” assumption was the UK would have enough supplies to meet heating and lighting demand.