BORIS Johnson has pledged £700m towards a nuclear power project in a bid to improve the UK’s energy security.

But campaigners have called for the public funds to be spent on insulating homes to reduce energy bills – while the Scottish Government has insisted “nuclear power is a bad deal for consumers”.

The outgoing Prime Minister claimed that the spike in gas prices driven by the invasion of Ukraine and used it to justify why new nuclear generation capacity is needed in the UK.

The new reactor at the Sizewell site in Suffolk is expected to be built in partnership with energy firm EDF and could power the equivalent of about six million homes.

The total cost of the Sizewell C project could be around £20 billion, according to reports.

It is not expected to begin generating electricity until the 2030s; the similar reactor at Hinkley Point C in Somerset began construction in 2016 and will not be online until 2027.

Speaking in his final major speech as Prime Minister, Mr Johnson said: “We need to pull our national finger out and get on with Sizewell C.

“That’s why we’re putting £700 million into the deal, just part of the £1.7 billion of Government funding available for developing a large-scale nuclear project to final investment stage in this Parliament.

“In the course of the next few weeks I am absolutely confident that it will get over the line.”

Mr Johnson, in a speech at Sizewell, said there had been a “paralysis over British nuclear energy”, blaming successive governments for failing to invest in new reactors.

“Yes, nuclear always looks – when you begin – it always looks relatively expensive to build and to run,” he said.

“But look at what’s happening today, look at the results of Putin’s war. It is certainly cheap by comparison with hydrocarbons today.”

He said that if the under-construction Hinkley Point C in Somerset was operating now “it would be cutting our national fuel bills by £3 billion”.

Even though energy is reserved to Westminster, the Scottish Government can veto nuclear developments in Scotland thought planning rules.

SNP ministers remain opposed to nuclear technology pointing to high costs and safety concerns – but the power is connected to the UK-wide grid.

Launching the energy security strategy in April, UK Energy Secretary Kwasi Kwarteng said the vision would include “more wind, more solar, more nuclear, more hydrogen – while maximising North Sea production”.

The Scottish Government will publish an updated version of its 2017 energy strategy, alongside a just transition plan in the autumn after delaying the spring publication.

SNP Energy Secretary Michael Matheson has previously insisted that “nuclear power is a bad deal for consumers”.

He added: “In 2016, Hinkley Point C nuclear power plant received a contract for different strike price of some £92.50 per megawatt power, which has now increased by some 25 per cent since then.

“Recent power price spikes underline the need to create better outcomes from energy investments, particularly those struggling with household finances.

“Internal analysis has identified that in 2030 alone, Hinkley could add almost £40 a year to a consumers’ bill whereas an equivalent offshore wind farm would reduce bills by some £8 a year.”

Greenpeace UK’s chief scientist Doug Parr said the £700 million announced for Sizewell C “could insulate huge numbers of draughty homes, and cut next year’s bills, instead of being thrown on to the slow-burning financial bonfire that is EDF, to increase our bills for decades”.

He added: “The contrast between these lumbering white elephants and the dynamic, cost-cutting, innovative technologies in the renewables sector could barely be more striking.

“While this down-payment on failure shows the Government hasn’t noticed, the market has, and investors have fled the nuclear sector.

“To get Sizewell done, the Government would have to step in and add the enormous costs of building reactors to the enormous costs consumers are already paying for their electricity.”

The “Boris bill” would be the Prime Minister’s legacy, he added.

Tom Greatrex, chief executive of the Nuclear Industry Association, welcomed the UK Government funding.

He said: "This announcement is another important step toward starting construction at Sizewell C, cutting gas, cutting bills and creating stable, secure well-paid jobs for people up and down the country."

He said it “should be the start of a new era of nuclear construction to ensure our energy security for the rest of the century”.

GMB union national secretary Andy Prendergast said the funding for Sizewell C was a “belated step in the right direction”.

“With energy prices going through the roof and all bar one of our nuclear power stations due to go off line by the end of the decade, this does at least provide some assurance on our energy security,” he said.

“Years of political failure to make the right decision on new nuclear means we are woefully unprepared for the energy crisis facing us today.

“This same inertia has resulted in a failure to secure our domestic gas supply.

“The real-world consequences of this lack of political courage are higher bills and risk of blackouts this winter.”