Rail industry leaders have proposed building a tunnel between Scotland and Northern Ireland to a group tasked with exploring ways to improve connectivity between the four constituent parts of the UK. High Speed Rail Group (HSRG) has proposed tunnelling under the Irish Sea between Stranraer and Larne in its submission to a review led by Sir Peter Hendy, who is expected to publish his interim report within weeks. The two towns are 31 miles apart but a preferred route for the tunnel, based on 120-year-old research by the Victoria engineer James Barton, would be diverted to avoid Beaufort’s Dyke, a 1,000ft deep trench in the Irish Sea. According to the HSRG, the tunnel would bind Northern Ireland closer to Great Britain and would “address problems in economic status of Northern Ireland post-Brexit”. A new rail connection between Carlisle and Stranraer would be needed and the width of railway track in Ireland may need to be altered, the proposal said. Jim Steer, an HSRG board member, said: “There is an urgent need for both new and improved transport links between the four nations of the United Kingdom, which have been systematically neglected for too long. “Cross-border travel markets for rail were growing strongly over the period to 2019. Travel generates economic value, but the opportunity for further economic stimulus from this source will be lost if transport network capacity constraints are not addressed. “Building on the transformative impact of HS2, HSRG are calling for these cross-border rail links to be addressed as a matter of urgency, safeguarding the strength of the whole of the UK economy in the years ahead.” The pitch submitted to the review claims the proposal has the backing of the Northern Ireland assembly and the Scottish parliament and that there is a “feasible path to its funding from the UK Exchequer that does not adversely impact on other transport funding”. A government spokesperson said: “We have asked Sir Peter Hendy to make recommendations on how to improve transport connectivity between Scotland, Wales, Northern Ireland and England. His recommendations will be published in due course.” The prime minister first suggested connecting Stranraer in Scotland to Larne in Northern Ireland by bridge three years ago, an idea that was widely derided by engineers. Experts raised concerns about the practicality of constructing a bridge across the stormy stretch of water, which is more than 1,000ft deep in places, and said would require dozens of support towers at heights “never achieved anywhere in the world”.