EDF Energy is to extend generation from four of its UK nuclear power stations by up to seven years, the company has announced.
Heysham 1 in Lancashire, and Hartlepool, 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 French firm is planning to build a new nuclear power station at Hinckley Point in Somerset but is still to make a final investment decision.
EDF said the decision 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."
The four nuclear plants employ over 2,000 permanent staff and 1,000 contractors.
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.
Greenpeace has said the delay means it is not certain that the final go ahead will be given. The campaign group said the project faces "unprecedented opposition" from EDF's management and French unions over costs.
The four nuclear plants which will generate power for longer, supply electricity to around a quarter of the UK's homes.
Mr de Rivaz added: "In today's extremely challenging market conditions, our belief that Government policy will be maintained and strengthened gives us the confidence to invest in our nuclear stations. This gives customers the best value low carbon electricity available.
"It's a great achievement by thousands of EDF Energy staff and partners in the supply chain who have worked so hard to show that we can deliver on performance, reliability and safety."
EDF 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."
The statement continued: "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."