BORIS Johnson’s plans for a multi-billion pound tunnel between Scotland and Northern Ireland have been slammed by a leading economic think-tank.

The Fraser of Allander Institute (FAI) said it would not deliver the economic benefits claimed, would clash with climate change objectives and the money could be better spent on other things.

The Prime Minister previously said serious consideration is being given to building a bridge between Portpatrick and Larne in Northern Ireland.

But last week Scottish Secretary Alister Jack said he favoured a tunnel – and claimed Mr Johnson is “on exactly the same page”.

He said a tunnel would boost the economies of both regions and strengthen the Union, and could be built by 2030.

And he claimed it would also better address some of the problems associated with the deep, stormy North Channel – part of which was used as a Second World War munitions dump.

He said: "It's no different to the tunnels connecting the Faroes, it's not different to the tunnels underneath the fjords, and it deals with the problem of Beaufort's Dyke and the World War Two munitions.

"The bridge for me is a euphemism for a link, which is a tunnel."

But the FAI dismissed the idea, which it noted was “not an April Fool”.

In a blog post, it said: “It won’t deliver the economic boost some claim, it isn’t a priority, it would go to the wrong location, it wouldn’t be consistent with climate change objectives, and the money could be better spent on other things.

“Apart from that, it’s a cracking idea.”

The FAI said those hoping the 21-mile road link would be a “catalyst for faster economic growth in both Scotland and Northern Ireland will be sorely disappointed”.

It said improving how people move around Scotland’s cities is a higher priority – and pointed out it still takes two and a half hours to travel between Aberdeen and Glasgow.

The think-tank said the proposed bridge or tunnel would not actually link up centres of economic activity.

It added: “Instead, travellers will arrive in rural Dumfries and Galloway or Argyll, with a 90+ mile drive to the central belt (at least a further two and a half hours).

“This won’t improve connectively to the point where any hope of clustering or agglomeration economic effects could be expected to take hold.”

The economists said the estimated cost of around £20 billion would be equivalent to more than 14 Queensferry Crossings and could be “far better spent”.

SNP MSP Tom Arthur said: “If Boris Johnson has £20 billion to spend on infrastructure then we’re happy to send him some suggestions.

“But, as the Fraser of Allander Institute rightly point out, a road bridge – or a tunnel – across the Irish Sea is hardly a priority.

“Boris Johnson couldn’t build a bridge across the Thames when he was London Mayor – but thinks we’re going to trust him to deliver one of the most complicated infrastructure projects imaginable.

“Everyone knows the Tories have no intention of delivering this – as always, this is just a way for Boris Johnson to distract from the failures of a decade of Tory austerity.

“If the Tories can’t explain why the Fraser of Allander Institute are wrong then they should be laughed out of every room where they mention this daft plan.”

Scottish Greens transport spokesman John Finnie MSP said the analysis "shows how utterly ridiculous Boris Johnson’s proposed bridge really is".

He added: "If there really is £20bn available for major infrastructure projects this could play a huge role in our efforts to tackle the climate crisis.

"We could renew Scotland’s entire public ferry fleet, support councils to establish local publicly owned bus services, and make much needed improvements to our rail network like redualling the Milngavie and Highland main lines and reopening the Dunfermline to Alloa route.

"It’s time for this Tory government to either put up or shut up, rather than perpetually droning on about this absurd road to nowhere.”