Up to a million households in England, Scotland and Wales will be paid to use less electricity tonight (Monday 23 January) as part of a scheme to avoid blackouts.
National Grid said the scheme, 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 or washing machine.
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.
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.
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, which allows some households to receive discounts if they cut their use of electricity, by, for example, delaying the use of a tumble-dryer or washing machine.
The scheme is available to homes with smart meters and whose energy supplier is signed up to it.
According to National Grid’s electricity system operator, 26 suppliers have joined the scheme, including British Gas, EoN, Octopus Energy and EDF, and 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.
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.
“These are precautionary measures to maintain the buffer of spare capacity we need,” it said.