A nuclear power station will stop generating electricity next February after 44 years because it would not be economically viable to continue after that time, it was announced today.
The reactor at Oldbury in Gloucestershire is the oldest civilian nuclear reactor in the world and has been generating power safely since 1967.
Operators Magnox and site owners the Nuclear Decommissioning Authority (NDA) said Oldbury will move through a transition period before decommissioning begins.
Phil Sprague, Oldbury site director, said: "Oldbury's excellent generation history is a terrific success story, especially as the site was originally planned to close in 2008.
"As a result of excellent teamwork between Magnox and the NDA, and in conjunction with our regulators, the ONR, the site's operational life was extended until February 2012. It is a testament to the skill and dedication of the workforce who have operated and maintained the reactors to such a high standard that it has been able to continue to generate safely.
"Oldbury has provided the UK with a vital source of power for over four decades, something that everyone who has worked at the site, past and present, should be very proud of."
It had been hoped the reactor would continue to generate electricity until the end of 2012.
Both of Oldbury's reactors were scheduled to close at the end of 2008, and since that time the site has generated an additional seven terawatt hours (TWh) of electricity, worth an estimated £300 million to the taxpayer and saving around six million tonnes of carbon from being released into the atmosphere.
Richard Waite, president, UK and Europe, at EnergySolutions, the owners of Magnox Ltd, said: "My congratulations go to Phil and his team who have worked so hard to deliver such a remarkable achievement.
"I am sure that when generation ends the workforce will bring the same skill and commitment to the successful and safe defueling and decommissioning of the station."
Mike Graham, national officer of the Prospect union, said: "To have been a consistent and safe source of vital electricity since 1967 is a record to be proud of and one that sends out a positive message in terms of future new nuclear plant at Oldbury.
"We recognise that the decision to bring forward the closure date was made purely on financial grounds, and congratulate staff for the diligence and expertise which has ensured the plant continued to operate past its original deadline of 2008, providing an additional £300 million to fund the NDA's decommissioning programme.
"The transition to defueling and decommissioning operations will mean an ongoing requirement for skilled staff on site. This continuity in employment will also ensure that there is a ready and willing skilled workforce in place in anticipation of the construction of the new Oldbury B plant."
Meanwhile, Unite called for an urgent debate on the UK's future energy needs, warning that the country was heading for an "energy crisis", with demand threatening to outstrip supply after 2015.
National officer Kevin Coyne said: "Sky-high energy bills are fuelling inflation but things could get even worse. The coalition Government's complacency on energy policy and innovation is driving the country towards an energy crisis.
"Power stations up and down the country are closing and the Government has shelved a world-beating, environmentally-friendly carbon storage project which would have eased the pressure. The technology would have also created thousands of jobs in the sector and its manufacturing supply chain.
"Energy costs are already sky-high and, as demand begins to outstrip supply, electricity bills will become even more expensive.
"The coalition Government has completely failed to get a grip on energy policy and displayed incompetence when it comes to supporting world-beating environmental technology which would ease the pressure. There needs to be urgent action."
A Department of Energy and Climate Change spokesman said: "Oldbury power station has made a significant contribution to the UK's electricity needs for 44 years. All who have worked there should be commended for generating power safely for over four decades.
"The Government has made clear the long-term role for nuclear in the UK's energy mix and this year finalised the Nuclear National Policy Statements, which identified eight possible sites across the country for nuclear new-build, including one at Oldbury which could create thousands of new and highly-skilled jobs.
"The proposals we have set out to reform the electricity market will deliver the best deal for Britain and for consumers, getting us off the hook of relying on imported oil and gas by creating a greener, cleaner and ultimately cheaper mix of electricity sources right here in the UK, nurturing a new generation of power sources including renewables, new nuclear, and carbon capture and storage, bringing new jobs and creating new expertise in the UK workforce."