EDF is to extend the life of four of its UK nuclear power stations and has made assurances that it is close to announcing a final decision on building a new plant at Hinkley Point.
The French energy giant said Heysham 1 in Lancashire and a plant in Hartlepool, both due to be decommissioned in 2019, will continue for an extra five years.
Heysham 2 and Torness in Scotland will have extensions of seven years to 2030.
The move will safeguard more than 2,000 direct jobs and some 1,000 contractors at the sites, which provide electricity for a quarter of British homes.
EDF, which is 85% owned by the French government, announced the extensions as it reported a 68% fall in profits last year and cut its annual dividend.
The company said it was committed to being the UK's leading investor in low-carbon electricity, adding in a statement: "That means safely extending the lives of existing nuclear power stations and investing in renewable wind energy.
"It also means making the big investments necessary to launch a renaissance in nuclear new build at Hinkley Point in Somerset.
"Further major progress was made in 2015 on plans to build a new nuclear power station at Hinkley Point in Somerset, notably with the signing of the Strategic Investment Agreement between EDF and China General Nuclear Power Corporation (CGN) in October.
"Hinkley Point C is a strong project which is fully ready for a final investment decision and successful construction. Final steps are well in hand to enable the full construction phase to be launched very soon."
Campaigners against Hinkley said the further delay in announcing a final decision cast doubt on the project.
Greenpeace policy director Doug Parr said: "EDF's accounts show growing debts and falling earnings. EDF management and employees warn taking on further risk could easily spell disaster for the company. Hinkley is a bad investment and most people with an ounce of financial acumen have now come to realise this.
"Chancellor George Osborne stands alone in defending Hinkley's honour. He needs to let Hinkley go - everyone else has. The nuclear industry has usually promised far more than it has delivered and the debacle over the Hinkley reactor shows little has changed."
There was industry speculation that a final decision was being held back over assurances being sought by the Chinese over the technology to be used at a planned new nuclear power station at Bradwell in Essex.
EDF said the decision to extend generation at four of its eight UK plants followed "extensive technical and safety reviews".
"Our continuing investment, our expertise and the professional relationship we have with the safety regulator means we can safely prolong the operating life of our nuclear power stations," said chief executive Vincent de Rivaz.
"Their excellent output shows that reliability is improving whilst their safety and environmental performance is higher than ever."
EDF has agreed a deal in principle for the £18 billion Hinkley project under which China General Nuclear Power Corporation (CGN) will pay a third of the cost.
Reports have suggested the company is struggling to find the cash for its stake.
Paul Kenny, general secretary of the GMB union, said: "It is inconceivable that the Hinkley Point C site should become the most expensive landscaped grounds in the UK if work is stopped and the project does not go ahead.
"If the plan to finance the building of this station by the French and Chinese governments is no longer viable then the UK Government has total responsibility to the people of this country to build the power stations needed to supply our electricity needs.
"The supply chain is in place and the labour force is coming on stream to construct this station essential to keep the lights on in the UK.
"The UK Government can no longer outsource the building of our power stations to foreign governments."
Dr Richard Dixon, director of Friends of the Earth Scotland, said: "EDF have announced the life extension for Torness because they are trying to distract attention from their terrible financial performance and their repeated failure to make a final decision on whether to build the Hinkley Point reactors in Somerset.
"Nuclear power is on its last legs in Europe and Hinkley will probably never get built."
Tom Greatrex, chief executive of the Nuclear Industry Association, said: " The plans to extend the life of four of the UK's nuclear power stations is welcome news for the local, regional and national economy.
"As well as providing secure, low-carbon electricity to millions of UK homes and businesses, lifetime extensions will help safeguard hundreds of skilled jobs in Scotland and the North of England."
Energy and Climate Change Secretary Amber Rudd said: "The extension of these four nuclear plants is part of our plan to deliver long-term energy security for our families and businesses - taking decisions today for the good of tomorrow and tackling the legacy of under-investment so that they have secure, affordable and clean energy supplies they can rely on in the years ahead.
"The UK is open for business and EDF's decision is a vote of confidence in our support for the nuclear industry. It will safeguard thousands of jobs, meaning more financial security for working people, and nuclear, as a low-carbon source of electricity, will also help us to reduce our emissions."
EDF chairman Jean Bernard Levy told a press conference in Paris: "We intend to proceed quickly with the final investment decision on Hinkley Point but there is a little work to complete, particularly because we could not finalise the discussions with our Chinese partners before their own break, before the Chinese New Year.
"There is still a little work to complete but, today, we believe that the final investment decision is very close."