… This is a dreadful agreement for the nation,” said Prof Catherine Mitchell, an energy policy expert at the University of Exeter. “The government is already paying a high price, index-linked for an incredibly long 35 years. This should be more than sufficient for a professional, business contract.

“The £22bn ‘poison pill’ effectively reduces the risk to zero for EDF and its backers, which is great for them. But from an outside perspective, it smacks of desperation.”

“There could be so many reasons over 35 years that you would want to close the plant,” she said, including rising costs, changes to the UK’s energy system or loss of public confidence. …

…Former Conservative energy secretary Lord Howell has criticised the Hinkley dealas “one of the worst deals ever” for British consumers and industry and has protested against “endless government guarantees for risk-free returns to the investors”.

Tom Burke at thinktank E3G, a former special adviser to three Conservative environment secretaries, said: “Why would a Conservative government want to buy 35 years of electricity ahead of time? They are supposed to believe in the market. But they have tied themselves in knots and now it is too embarrassing to untie it.”

The UK government argues that new nuclear power is essential to provide large amounts of reliable, low-carbon energy.

But Mitchell said: “Energy economics are changing rapidly and so the momentum is towards decentralised, smart and flexible energy systems. It is moving away from large, inflexible power plants like Hinkley. If it ever gets funded, it will be a white elephant before it is even finished and this government, with this £22bn ‘poison pill’, will have tied the next generation into paying for it, for no reason that I can understand. If it is simply political saving face, it really is pitiful.”