Could a cross-Irish Sea link be a bridge too far?

24th February 2021

A new report, commissioned by the Prime Minister and headed up by Network Rail Chair Sir Peter Hendy, will shed light on the ‘cost, practicality and demand’ of a Scottish-Northern Ireland link, as well as review transport connections across the UK in general.1 Here, we hope to find out what purpose such a link would serve, the criticisms levied against the idea, and the feasibility of such a project. As demonstrated by Sir Hendy’s imminent report, improvement of transport links between all four countries of the Union is desperately needed and has been described as being ‘systematically neglected’ by High Speed Rail Group (HSRG) board member Jim Steer.2 


Whilst efforts to improve connectivity are in place between each constituent nation on the mainland through projects such as the ‘Northern Powerhouse’ and HS2, the same efforts are not present to connect Northern Ireland with the mainland. To remedy this, a proposed cross-Irish Sea link would significantly cut the crossing time from two-and-a-half hours on a ferry to 40 minutes via a tunnel.3 It would appear that a cross-Irish Sea link would be economically advantageous, not just for Northern Ireland and Scotland but also for the North of England, especially post-Brexit, with the creation of a ‘Celtic powerhouse’ having previously been touted.4 In support of this, both HSRG and the transport think tank ‘Greengauge 21’ have been vocal about how such a link would help to open up and develop south west Scotland. As part of this development, the most popular of the proposed routes, a 31 mile-stretch between Stranraer and Larne, could see additional investment in the Dumfries Railways and Stranraer to support the connection, including additional infrastructure at an airport which could be used as an entry point to the route.5 The link could then become part of a larger ‘capital cities axis’ linking Dublin, Belfast, Glasgow and Edinburgh, in turn aiding the development of key border hubs such as Carlisle due to its connections to Leeds and Newcastle.6 


There are challenges to building a link across a 25-mile stretch of sea, foremost of which are the 200-metre deep waters. 7 In addition to this, the most direct route crosses a 300m trench, Beaufort’s Dyke, previously used as a munitions dump by the Ministry of Defence and estimated to contain one million tonnes of volatile chemical and conventional munitions.8 Alongside the depth of the sea, and the munitions dump, the use of a single bridge to connect the two countries also poses the issue of ship collisions. Whilst technically feasible, the consensus has been that an underwater tunnel for sections of the route would be most suitable, with a bridge alone being ‘eye wateringly expensive’.9 Despite previous experience in the form of the 31-mile Channel Tunnel (23.5-miles of which is underwater), a similar design under the Irish Sea would be both time consuming and expensive, due to the harder materials under the Irish Sea as opposed to the relatively soft chalk between Britain and France.10 A more cost-effective alternative would be a ‘floating tunnel’ concept, currently promoted by Heriot-Watt University, that would involve a ‘submerged floating tube bridge’ anchored to the sea bed and tethered by pontoons on the surface.11 Any finished design would most likely draw upon both bridge and tunnel sections to utilise the respective advantages and disadvantages of each, using other similar projects, such as the Øresund Bridge between Denmark and Sweden, for inspiration. 


Inevitably, political consideration will also play a role in the future of a cross-Irish Sea link, with Westminster already criticised for undermining the devolution process by both Scotland’s Transport Secretary and Northern Ireland’s Minister for Infrastructure due to ‘virtually no consultation’ being offered on the project.12 


The Institution of Civil Engineers (ICE) has placed the cost of a rail-only tunnel between Stranraer and Larne at £12bn, and a road-only bridge at £24bn. However, ICE have said that completion of a bridge could take 15 to 20 years, with costs increasing to £40-50bn.13 Whilst the building of a cross-Irish Sea link post-Brexit certainly has its advantages, there is a fine tightrope that needs to be approached with care between prioritising long and short-term investment and development, with public value-for-money and the involvement from Westminster and all devolved parliaments as paramount in this decision.