Kingsnorth coal-fired power station in Kent is to close in March 2013, E.ON said on Thursday, with the loss of 123 jobs.
The plant, which generates enough power for nearly 2m homes, will be forced to shut because it will have run out of its allocated operating hours under EU environmental legislation.
Under the Large Combustion Plant Directive (LCPD), polluting power stations that were not adapted to meet emissions-reduction targets will have to close by the end of 2015, or when they use up an allowance of 20,000 generating hours from 1 January 2008 - whichever comes first.
Data on hours of generation is made public and the closure of Kingsnorth in 2013 was widely expected within the industry, but today is the first official confirmation of the timescale.
E.ON said: "The 1,940MW coal-fired power station, originally commissioned in 1970, will have reached the end of its allocated running hours by March next year and will be taken off-line."