The buffer was higher than a margin of 8.8 per cent of peak demand last year, or 5.2GW, a 900 megawatt increase equivalent to the output of about three gas power stations. Neso said that the average demand during peak cold spells was expected to be 60.9GW, below an expected 67GW of available supply.

Electricity demand is expected to ­exceed supply for less than 0.1 hours a year under normal operations. However, the operator warned that there may be a "small number" of "tight days", most likely in early December or mid-January, but excluding the ­Christmas period, which could be caused by periods of extremely cold weather and low wind, low interconnector imports and high levels of generator outages.

National Gas also cautioned that while Britain had sufficient gas supply to meet its needs, some "high peak ­demand days" were still expected. Overall gas demand this winter is ­forecast to be 3 per cent lower than last year, mainly due to reduced power ­consumption.

In the event that the amount of available electricity generation falls below 500MW of peak demand, Neso can issue a notice to the energy market ­asking for a greater cushion of supply. The systems operator models about 30,000 factors including weather, power plant outages and lower imports. Weather simulations are based on data from 1987 to the present day.

The margin is slightly lower than the 10.9 per cent buffer projected in Neso's early winter outlook in June, reflecting longer hydropower plant outages.

In a worse-case scenario where power generation or imported electricity is 4GW lower than its base case forecast, there would still be a supply margin of 3.4GW, or 5.5 per cent of peak demand.

The increase in the buffer represents another step of recovery in Britain's energy security after Europe was plunged into an energy crisis after the outbreak of the Ukraine war, after which the margin shrank to 6.6 per cent of peak demand in the winter of 2022.

However, average household energy bills remain hundreds of pounds higher a year than pre-war levels. At the start of this month, the typical dual-fuel bill increased to £1,755 a year, after Ofgem, the energy regulator, raised the price cap by £35, or 2 per cent, compared with the previous quarter.