Experts to look at feasibility of building £20bn 'Union Tunnel' between Scotland and N Ireland

The report also includes the launch this spring of a consultation on cutting air passenger duty on internal UK flights.

Today, the Scotland-Northern Ireland “fixed link” issue is expected to be raised by Boris Johnson at Prime Minister’s Questions in the Commons and at Scottish Questions, preceding it, by Alister Jack, the Scottish Secretary, as part of the UK Government’s drive to strengthen the Union in the face of calls by the SNP for a second referendum on Scottish independence.

"It’s now time to build back better in a way which brings every corner of the UK closer together,” declared Mr Johnson.

“We will harness the incredible power of infrastructure to level up parts of our country that have too long been left off the transport map.”

He stressed: "This pioneering review by Sir Peter Hendy gives us the tools we need to deliver on our ambitions for a UK-wide transport network that encompasses sea, rail, and road and I also want to cut passenger duty on domestic flights so we can support connectivity across the country.”

In his interim report, Sir Peter says, as well as a wider review of transport links across the UK, he has been “asked specifically” to look into the fixed link idea, first proposed by Mr Johnson in summer 2018 as a bridge.

After he became PM, Mr Johnson commissioned the Union Connectivity Review last June.

Since then, it is thought that the prospect of a bridge has receded given the bad weather across the Irish Sea would close it for four months of the year. The preferred option now is a £20bn undersea tunnel, described by Mr Jack in a Herald interview in January as a “fantastic” idea but dismissed by political opponents as a “vanity project”.

Yet even a plan for an underwater tunnel would have to contend with the potential problem of unexploded WW2 ordnance on the sea-bed.

In his draft report, Sir Peter says he has asked two experts, Professor Douglas Oakervee, and Professor Gordon Masterton, both past presidents of the Institution of Civil Engineers, to “lead a discrete piece of work, using engineering consultants, to assess the feasibility of such a link, and an outline cost and timescale for the link and the associated works needed”.

Prof Oakervee is also a past Chairman of both HS2 and Crossrail while Prof Masterson is a past President of the Institution of Engineers and Shipbuilders in Scotland and is the Chairman of Future Infrastructure at Edinburgh University.

The report says a UK Strategic Transport Network would significantly expand and upgrade direct transport connections in the UK across road, rail, sea and air, helping to reduce delays and bottlenecks and stimulate economic growth.

To jump-start some of the projects identified in it, the Government has today committed £20m towards exploring their development. They include:

*upgrading the A75 between Gretna, Dumfries and Stranraer, a key route for south-west Scotland and Northern Ireland but almost entirely single carriageway;

*significantly faster rail links from Scotland to England, including looking at options to enhance the West Coast Mainline and

*improved rail connectivity between the north coast of Wales and England.

The UK Government has made clear it wants to work with the devolved administrations in building up the UK Strategic Transport Network.

However, Whitehall sources have told The Herald that there has been a reluctance from the Scottish Government to engage in Sir Hendy’s review. “It has the word Union in it,” noted one well-placed insider.

The full report is due to be published in the summer ahead of the UK Government’s autumn Spending Review, which will consider and confirm funding plans for delivering improved connectivity across the UK.