Plans for Sizewell C are doomed to “evaporate” in the wake of insurmountable problems that will prevent its intended forerunner at Hinkley Point ever producing electricity, one of Britain’s leading environmentalists has predicted.

The Chinese and French-financed nuclear construction project on the Somerset coast “might get started” as Theresa May’s government tried to “save face” but the £18billion twin-reactor mega-project was destined to become mired in construction difficulties and delays. It would eventually be overtaken by burgeoning renewable energy technologies in which numerous important breakthroughs were being achieved, green heavyweight Sir Jonathon Porritt told a public meting in Aldeburgh’s Jubilee Hall.

“The government is committed to a nuclear renaissance which has a price tag that nobody can actually quite believe,” Mr Porritt said. “Hinkley Point has a price tag which has to stagger belief and yet we are increasingly coming to understand that we really don’t need this renaissance anyway as we have another renaissance going on in terms of renewable energies.”

The European Pressurised Water Reactor (EPR) design planned for Hinkley was seen by some nuclear industry experts as being “unconstructable because of its complexity”. The EPR complex at Flamanville, north-west France, was beset with construction delays and spiralling costs – and yet there was thought to be a clause in the government’s Hinkley deal that said that unless Flamanville was producing electricity by 2020 all undertakings given to the French giant EDF Energy for the Somerset scheme would become “null and void”.

The meeting, organised by Together Against Sizewell C, was told by Mr Porritt: “I do not believe Hinkley Point will ever produce electricity. It might get started because the government is so committed to it and wrapped up in it and wants to save face, but I don’t believe it will generate electricity.”

Nuclear power technology was “desperately old and tired” and was “incapable of meeting our needs for the future”, he said. “It cannot compete against the new energy paradigm that is there for us today.”

An inescapable conclusion over the government’s perseverance with it was that it offered the skills base needed for Britain to maintain its nuclear weaponry. The “mega irony” in this was that George Osborne had gone to Beijing five times with “the world’s biggest begging bowl” when he was chancellor and the “potentially aggressive hostile” China had been invited to “join the mix” of Britain’s energy infrastructure.

“You just couldn’t make it up,” said Mr Porritt, who has held many high-profile environmental positions and is founder-direct of the international Forum for the Future. “This is a macro irony – a mega irony – but there is no other explanation for what has happened. People will get wise to it and Sizewell C will evaporate,” he said.

EDF Energy told the EADT it had completed the first of a “multi-stage public consultation for Sizewell C” and was “moving towards the next stage of consultation for the project”.

It said: “The EPR reactor, to be used in Sizewell, has already been through the Generic Design Assessment process and approved by the Office for Nuclear Regulation.

“The EPR is closely based on proven pressurised water reactor (PWR) technology and it is the only reactor design that has been through the Generic Design Assessment process. There are 277 PWRs operating around the world, including 58 in France, and Sizewell B in the UK. This means the EPR design draws on several thousand years of operational experience from similar reactors.

“Our robust construction plan for Hinkley Point C has been developed with early involvement of contractors. Planning and 4D modelling already undertaken has helped make construction planning more efficient.”

Hinkley Point C is due to start producing electricity in 2025. EDF says it will “provide reliable, low-carbon electricity to meet 7% of the UK’s future electricity needs” and would be a “major step forward in the fight against climate change”.