Stop Sizewell C had challenged the new nuclear power station

Mrs Justice Lieven dismissed the claim brought by the action group Stop Sizewell C, under the name Theberton and Eastbridge Action Group, that the boundary for the nuclear site licence did not cover sea defences and flood barriers, vital for future site safety.

Following a hearing at the High Court, she said the legal action had "no chance of success" and was "totally without merit".

She added: The fundamental argument advanced by the claimant is, in my view, plainly wrong.”

Campaigners waving banners and placards had gathered outside the London court on Tuesday morning to hear the outcome of the legal action.

Stop Sizewell C said the reason for the challenge was to keep the Sizewell C site safe from rising sea levels well into the future.

The group said new flood barriers being proposed to the north and south of the site were not included in the original planning permission or were part of the planning examination.

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Sizewell C, sited on the "vulnerable" Suffolk coast, needed a "Hard Coastal Defence Feature and Soft Coastal Defence Feature" to mitigate the impacts of climate change, the campaigners said.

Paul Collins, of Stop Sizewell C, said: "We are disappointed and surprised that the court concluded that the 1965 Nuclear Installation Act did not require the imposition of a condition, when the Sizewell C nuclear site licence was granted, to deal with a safety issue - namely the sea defences - that was well known at that time.

"The judge fully acknowledged that the sea defences are critical for the safety of Sizewell C's reactors."

Alison Downes, also of Stop Sizewell C, added: "It remains the case that we are deeply concerned about this issue.

"There is still no final design of the sea defences let alone guarantees that the construction is feasible.

"We thank our legal team and supporters and are considering our position."