Boris Johnson has given his blessing to a review exploring a multi billion-pound rail tunnel between Scotland and Northern Ireland.
Sir Peter Hendy, chairman of Network Rail, has asked experts to conduct a review of a potential tunnel between Stranraer and Larne.
Doug Oakervee, the author of a Government-commissioned report that gave HS2 the green light earlier this year, will lead the analysis.
Sir Peter said: “If you look at the distance between Northern Ireland and Scotland it is actually no further than the Channel Tunnel.
“I said to Boris, I am not going to get any further than finding out whether it is feasible, how long it will take and how much it might cost."
The Prime Minister appointed Sir Peter to conduct a wider “Union connectivity review” in June to assess improvements to transport links between England, Scotland, Wales and Northern Ireland.
Last September Mr Johnson asked civil servants to consider the building of a 21-mile bridge between Northern Ireland and the British mainland at an estimated cost of £20bn.
Scottish ministers said in March that Downing Street had now asked them to look at a tunnel amid fears that high winds would close a bridge crossing for up to 100 days-a-year.
A key plank of the Convervatives' general election pledge to level up the economy was boosting regional connectivity.
Fears have mounted, however, that the coronavirus pandemic has put this priority on hold - not least when ministers’ refused to bail out regional airline Flybe in March.
Sir Peter, who led Transport for London under Mr Johnson when he was London mayor, told the Railway Industry Association annual conference: “The Government’s policy is to bring the United Kingdom closer together. The quest for economic growth, particularly in the light of Brexit, is a common desire for Westminster and for the developed administration governments.
“If you look at air and ferry connections, one of the current bugbears for Northern Ireland is that since Flybe went bust there is much less opportunity to fly into Northern Ireland. They clearly find that very difficult. Maybe I can look at that and do something about it.”