A coal-fired power station in north Yorkshire has announced it will stop generating next March, with the loss of 240 jobs.
The owners of Eggborough Power Station near Selby said it would take £200m of additional funding over the next three years to continue generating power, which was "financially unsustainable" for the 53-year-old plant.
The station had previously failed to gain government support to convert to biomass and its owners said it had now taken the "difficult decision" to start consultations with staff over redundancies, although it said there will be some work to support decommissioning.
Neil O'Hara, chief executive of Eggborough Power, said: "We are deeply saddened at the prospect of potentially ceasing generation at Eggborough Power Station and believe that Eggborough Power could have a significant part to play in ensuring security of supply in the UK electricity market, particularly while there remains great uncertainty around new-build gas-fired generation.
"We intend to conduct a thorough consultation process with our employees and their representatives while we continue to consider all options available to us, including seeking to engage with government bodies. Our priority is to support our staff during this difficult time."
Falling power prices, high carbon taxes and uncertainty over environmental permits were among a variety of regulatory conditions, blamed for the move by the company.
An Energy Department spokesperson said: "This is obviously disappointing news for everyone connected with Eggborough, but people can be assured that energy security will be unaffected.
"The Government takes security of supply very seriously and has worked with National Grid to put in place an effective plan which is flexible enough to adapt to individual plant closures.
"Our top priority is making sure UK families and businesses have secure, affordable energy supplies - we have ensured that National Grid have everything they need to manage the system."
Regional officer for the Unite union Kelvin Mawer said: "What has happened to the coal-based energy sector in West Yorkshire in recent months is devastating to those losing their jobs and a crippling blow to the local economy.
"Energy secretary Amber Rudd should take a long, hard look at the energy needs of the country. Coal is the cheapest form of energy, especially if the carbon tax was lowered. Britain is sitting on a huge reservoir of coal.
"By closing Eggborough and Ferrybridge C, you are reducing their contribution to the grid by about 8 per cent, enough to power about four million homes. If there is a harsh winter this year, we believe that energy demands will be so stretched, power cuts could be on the cards."