The giant plant in southwest England was to open a year later than earlier planned and cost up to an extra pound3 billion ($3.7 billion, 3.5 billion euros), constructor EDF -- the French electricity giant -- said Thursday.

EDF blamed the delays on fallout from the Covid pandemic, while costs have shot higher as inflation soars worldwide.

The UK government on Friday said Hinkley was a necessary part of Britain safeguarding its energy security, which it has recently stressed following the invasion of Ukraine by key energy producer Russia.

"While the Covid pandemic has understandably led to delays, the revised Hinkley Point C construction forecast will have no impact on British billpayers or taxpayers, with any increase in costs borne entirely by the developers," said a UK government statement.

"We will continue to work closely with EDF to bring Hinkley Point C to completion, the first new nuclear power station in a generation, which has created and supported over 22,000 jobs across the UK."

The statement added that "new nuclear power is essential to the UK's energy security, providing clean and affordable homegrown power".

The total cost of Hinkley, which aims to provide seven percent of Britain's total power needs, had already swelled to as much as pound23 billion and had been due to begin generation in June 2026, already well behind schedule.

Hinkley Point is Britain's first new nuclear power plant in more than two decades.

EDF on Thursday said electricity generation at the plant was now forecast to begin in June 2027, "assuming the absence of a new pandemic wave and no additional effects of the war in Ukraine".

It added that costs were now estimated between pound25 billion and pound26 billion.

"During more than two years of the Covid-19 pandemic, the project continued without stopping. This protected the integrity of the supply chain and allowed the completion of major milestones," the French group said in a statement.

"However, people, resources and supply chain have been severely constrained and their efficiency has been restricted."

EDF added that the cost of materials, engineering and in particular marine works had risen.

- 'Risky and expensive' -

Britain has 15 nuclear reactors at eight sites but many are approaching the end of their lifespan.

However, the current government wants to maintain the 20 percent of electricity it generates from nuclear to help meet its pledge to reduce carbon emissions to net zero by 2050 and tackle climate change.

Critics have focused on the proposed design, which uses a new European Pressurised Reactor system that has been beset by huge cost overruns and delays at sites in France and Finland.

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