Proposed British Isles fixed sea link connections

Such a project was considered by railway engineer Luke Livingston Macassey in the 1890s as "a rail link using either a tunnel, a submerged "tubular bridge" or a solid causeway".

[10] The Eastern basin of the Irish Sea between the Isle of Man and Great Britain is significantly shallower than the Western side.

[13] Captain Macbay's reasoning for the necessity of a fixed Irish Sea connection (either by tunnel, bridge or causeway) are summarised in seven points.

[16] In 1897 a British firm applied for £15,000 towards the cost of carrying out borings and soundings in the North Channel to see if a tunnel between Ireland and Scotland was viable.

[17] The link would have been of immense commercial benefit, was significant strategically and would have meant faster transatlantic travel from the United Kingdom, via Galway and other ports in Ireland.

[citation needed] When Hugh Arnold-Foster asked in the Commons in 1897 about a North Channel tunnel, Arthur Balfour said "the financial aspects ... are not of a very promising character".

[18] In 1915, a tunnel was proposed by Gershom Stewart as a defence against a German U-boat blockade of Ireland but dismissed by H. H. Asquith as "hardly practicable in the present circumstances".

[19] In 1918, Stewart proposed that German prisoners of war might dig the tunnel; Bonar Law said the Select Committee on Transport could consider the matter.

[25] In 1997–98, the Department of Public Enterprise refused to fund a feasibility study requested by the engineering firm Symonds to build an immersed tube tunnel.

[42] It was also reported in February 2021 that a proposal was considered by the government relating to an underground roundabout to be built under the Isle of Man to link Liverpool, Heysham, Stranraer and Larne.

[43][44] The Hendy Review published in November 2021 which looked into the proposals claimed that the cost of the fixed link, in either a bridge or tunnel form, was "impossible to justify" in this area given the sea depth, Beaufort's Dyke, and though noted "the economic viability of the provision of such a link is not within the scope of [the] study", recommended that it would regardless take too long to recoup the costs to justify further research.

[45] In May 2021 the then British Transport Secretary Grant Shapps discussed the case for a tunnel between Holyhead and Dublin along the Irish Mail route.

[47][48] Although the tunnel would be longer than the length of the proposed Irish Sea Bridge, the water in this area is shallower, and there are less obstructions (such as Beaufort's Dyke).