Homes across the UK could face the first energy blackouts in decades this winter if power plants can't get enough gas to keep running.

The National Grid Electricity System Operator (ESO) has urged people to help avoid lights going out, saying "save money and back Britain", by using more energy during off-peak times.

Households and businesses could face three-hour outages to ensure the grid did not collapse, in what has been described as an "unlikely scenario".

What would cause the blackouts?

Blackouts hit the UK during the 1970s in response to the miners strikes and the oil crisis.

This year, in the face of the “challenging” winter facing European energy supplies following Russia’s invasion of Ukraine, the ESO is planning for the different scenarios we could face this winter.

Lights will stay on unless the gas-fired power plants that produced 43pc of Britain’s electricity over the last year cannot get enough gas to continue operating.

If cold snaps happen early in the winter when storage sites are still relatively full they can supply all of the extra gas needed.

But if it happens later in winter when storage levels are low the UK will need to import more gas from the continent.

It is the most dire of three possible scenarios that the ESO laid out on Thursday for how Britain’s electricity grid might cope with the worst global energy crisis for decades.

What can be done to help?

To tackle a loss of imports from France, Belgium and the Netherlands, there are two gigawatts of coal-fired power plants on standby to fire up if needed to meet demand.

National Grid Gas Transmission separately said that while gas demand will increase this winter, it expects Britain to be able to get enough gas to take it through a Beast from the East scenario or a long, cold winter.

People are being encouraged to sign up with their electricity supplier to a scheme which will give them money back on their bills to shift their use of power away from times of high demand to help prevent blackouts.

Households tend to consume a fifth of their daily energy between 4pm and 7pm, according to data from Ovo Energy. The supplier on Thursday said its customers could save £100 if they signed up to use energy at off-peak times.

The “demand flexibility service” will run from November to March, and it is expected to swing into action 12 times whatever happens to ensure people get rewarded for being part of the scheme – with additional use if needed to protect supplies.

It is hoped it will deliver 2GW of power savings to balance supply and demand.

The ESO’s director of corporate affairs, Jake Rigg, said: “The demand flexibility service is a first of its kind and a smart way for signed-up consumers in homes and businesses to save money and back Britain.

“If you put your washing machine or other electrical appliances on at night instead of the peak in the early evening, you can get some money back when we all need it.

“The service is due to launch in November, so watch out for further details soon. This really is a window into the future where a flexible energy system will be cleaner and lower cost to alternatives.”

How likely are blackouts to happen?

Responding to the winter outlook, a government spokesperson said: “The UK has a secure and diverse energy system.

“To strengthen this position further, we have put plans in place to secure supply and National Grid, working alongside energy suppliers and Ofgem, will launch a voluntary service to reward users who reduce demand at peak times.”

However, Adam Bell, former head of energy strategy at the Department for Business, Energy and Industrial Strategy, has said the possibility of blackouts is high in the coming months if there is a cold winter and the situation in Ukraine does not change.

He said: “The chances of a very cold January itself are quite low. But given the constraints Europe is under, given the constraints our system is under, even with the interventions the National Grid already have planned you would likely see some rolling blackouts for domestic customers.”