High carbon prices and transmission charges will see Longannet coal-fired power station close next year, operator ScottishPower has confirmed.
The move was prompted by the National Grid's decision not to award the station a grid-balancing contract under a new scheme that sees plants due to be closed or mothballed continue to provide reserve capacity during the winter months.
The plant has been producing power for 46 years and currently employs 236 people, but will now close on March 31 next year as it has become "uneconomic". The operator said "a number of opportunities will be available for redeployment".
Neil Clitheroe, chief executive of retail and generation at ScottishPower, said: "This is a sad day for ScottishPower and for our highly-skilled and committed team at Longannet. We have explored every potential option to keep the station open and we still maintain that Longannet could continue generation in to the next decade under the right economic conditions.
"Our main focus now is consulting with staff to ensure we find the best outcomes possible for all of the 236 impacted employees, many of whom have spent their entire career at the station."
ScottishPower also confirmed that plans for a new gas-fired power station at Cockenzie, East Lothian, have been scrapped "due to the same economic conditions".
WWF Scotland director Lang Banks said the closure of the coal-fired plant was "inevitable".
"This announcement marks an historic, but important step in Scotland's energy transition," he said. "While Longannet has served the nation for many years, it is Scotland's single biggest source of climate emissions and a combination of its age, air pollution rules, carbon pricing and transmission charging have made closure inevitable.
"The recent Scottish Parliament inquiry into energy security provided ample evidence from the National Grid and other experts that Scotland's electricity supply is absolutely secure without Longannet.
"Indeed, Scotland will continue to remain a net annual exporter of power to the rest of Great Britain and an integrated part of the most secure electricity grid in Europe."
Richard Hardy, a negotiator with trade union Prospect, said: "The news is a body blow not just to Prospect members at the plant and the economy of West Fife and the Forth Valley, but also to Scotland's hopes of remaining self-sufficient in energy generation.
"It is extremely disappointing that, despite the efforts of Scottish Power and the Scottish Government, it has not been possible to put in place ways of keeping Longannet open until its original planned closure date of 2020.
"National Grid has forecast very tight margins for power supply this winter so removing a station that generates enough electricity for two million homes is senseless.
"Our members are paying the price for a mechanism that rewards companies building power stations near to London and penalises those in Scotland. Scotland generates 12 per cent of the UK's total power yet pays 35 per cent of the transmission charges. That is not a good deal for either companies or the customer."