The GMB union has accused the government of complacency over the UK’s energy supplies following a series of power station closures.
It said that nine stations are due to shut their doors by the end of 2016, but few replacement facilities are in construction. Furthermore, new nuclear sites such as Hinkley Point C in Somerset, which could make up some of the shortfall, will not start generating power for years.
The GMB, which represents thousands of workers in the energy sector, also noted that environmental standards are restricting the coal stations from coming online.
Brian Strutton, GMB's national energy officer, said: "If peak demand were to coincide with a time the wind is not blowing, the UK will have just 63GW of reliable, easily dispatchable power.
"The Government has stated that interconnectors, renewables and demand-side response can deal with any shortfall. However the first two cannot be relied upon at a time of system stress and demand-side is unlikely to cover a major shortfall.
"Breakdown or outages at existing stations could lead to a major shortfall and widespread power blackouts. No Government can rule out breakdown or outages at existing stations."
The concerns are raised on the day that National Grid publishes its winter outlook, which is expected to say that there is no threat to power in the coming months.
However, an assessment in the summer by the company showed that the UK would need more contingency measures than last year to ensure the lights stay on.
It said that the gap between total electricity generating capacity and peak demand would fall to just 1.2 per cent without measures in place such as paying inactive power plants to remain on standby ready to come online if needed.
With those extra measures in place for times of peak demand, the capacity margin rises to 5.1 per cent, the assessment showed.
Doug Parr, chief scientist with Greenpeace, said: "Every winter we're told our energy infrastructure will struggle to cope with a cold snap, and every winter energy firms are knocking on the Government's door for more handouts.
"The only way to awake from this groundhog day is to recognise that, as we transition to clean energy, the best way to keep the lights on is a major expansion of local and decentralised energy in our towns and cities.”
Eggborough Power Station (above) is one such plant that is due to close in March 2016. 240 job losses will be sustained from the shutdown although its owners have entered talks with a biomass firm to consider converting the plant to avoid the closure.
Last week, the final fuel element was removed from Oldbury Nuclear Power Station, marking the end of a process that began in 2012.