For some it's a noble project of national connectivity and engineering genius; for others, it's an inconceivably expensive fantasy designed to distract from real issues.

Views on a potential tunnel or bridge crossing the Irish Sea to link the islands of Ireland and Britain vary wildly. But the megaproject remains an apparent goal of UK Prime Minister Boris Johnson after a government report published on Wednesday said an official feasibility study will now take place.

Bridge vs. tunnel

History irrevocably links Ireland and Britain, but even though the six-county statelet of Northern Ireland is officially part of the UK, a physical connection between the two has never been attempted.

Various ideas have been mooted and discarded since at least the 1880s but the latest attempt stems from last summer, when Johnson announced a Union Connectivity Review, looking into transport links around the UK.

Britain's High Speed Rail Group (HSRG), a rail industry representative body, submitted a proposal to that review

calling for a rail link to be established between Scotland and Northern Ireland.

The suggestion of a bridge has been widely dismissed as unworkable. The weather and sea currents in the Irish Sea are two major reasons. An even more convincing reason is the fact that the British government is estimated to have dumped around 1 million tons of unused, still explosive munitions in a 50-kilometer (31-mile) underwater trench in the area called Beaufort's Dyke.

As a result, the tunnel idea, sometimes jokingly referred to as the Boris Burrow, has become the preferred option of proponents.

The idea has prompted both enthusiasm and derision from politicians either side of the Irish Sea over the past few months. But the now published interim report of the Union Connectivity Review keeps the idea alive, at least with the news that the UK government has appointed two engineering professors to undertake a technical review of the project.

Bridging the post-Brexit divide

However, the focus of the 61-page report suggests there are more pressing transport priorities in the UK. Just two lines in the report are devoted to the project. They come in chairperson Peter Hendy's foreword, where he announces a review "to assess the feasibility of such a link, and an outline cost and timescale for the link and the associated works needed."

The review will likely placate political supporters of the idea, even if it never becomes a reality.

Unionist (pro-UK) politicians in Northern Ireland, such as the hard-line DUP, are fervent supporters. Given that political party's anger over trade complications arising from Brexit and the Northern Ireland Protocol, Johnson's government may be keen to show unionist politicians in Northern Ireland that they are genuinely interested in exploring the viability of the project.

A question of liquidity

"If expense wasn't an issue, I think it would be a great project. It would be a tremendous thing," Trevor Orr, an adjunct professor at Trinity College Dublin who specializes in tunneling and geotechnics, told DW.

However, he points out that costs would be huge — "at least €20 billion" — and adds that the construction of a 45-kilometer (28-mile) underwater tunnel would take several years and would likely be beset by "objections, problems and delays."

"I think the cost benefit would be hard to justify," he said.

Technically though, he believes it is possible to successfully build an underwater rail tunnel linking Scotland with Northern Ireland. He points out that the early proposals have focused on a 1901 study by the engineer James Barton, who identified a potential underwater route which would largely avoid Beaufort's Dyke.

Orr believes the best option would be a tunnel traveling entirely under the seabed. He points to other underwater rail tunnels such as the Channel Tunnel and Japan's Seikan Tunnel, which at 54 kilometers is longer than what would be required to link Northern Ireland and Scotland.

"There is nothing really innovative needed that I am aware of," he said. "The thing is, it's a matter of how much you want to spend on it. Any of these engineering projects, certainly one like this, is technically feasible."

Money for 'pipe dream' better spent elsewhere: opponents

Even with an unlimited budget and a bounty of goodwill, completing such a project would be a mammoth task. But budgets are far from unlimited and opinion on the project is sharply divided.

The Financial Times has reported that officials in the UK Treasury see the project as an "impractical pipe dream," a view likely informed by the huge costs and the fact that the British economy is grappling with the effects of Brexit and the pandemic.

On top of that is the fact that responsibility for transport across the UK is devolved, meaning the assemblies in Scotland and Northern Ireland could potentially block the project.

Scottish First Minister Nicola Sturgeon has said she believes such an amount of money could be better spent elsewhere. In Northern Ireland, nationalist politicians are firmly opposed to the idea and are angry that Johnson's government has bypassed the Northern Ireland Assembly to propose the technical review.

Nichola Mallon, an Irish Nationalist politician with the SDLP party and the Northern Ireland minister for infrastructure called the technical review "a total breach of trust."

"I have consistently made clear that the enormous resource required to establish a fixed link bridge or tunnel could be much better spent addressing the priorities of people in our communities," she said. "I am bitterly disappointed with the attitude of the British government, which is obsessed with centralizing spending power in areas of devolved responsibility."

Northern Ireland Deputy Prime Minister Michelle O'Neill from the Nationalist Sinn Fein party, said: "The pipe dream bridge between the North and Scotland is a smokescreen for the Brexit fallout amongst the unionists who engineered it on both sides of the Irish Sea."

Tunnel can't change Brexit

Those on the other side of the debate will now await the technical review to see if the project goes any further.

In its original submission, Britain's High Speed Rail Group said a rail link would help "address problems in economic status of Northern Ireland post Brexit."

When asked by DW for more information as to how a rail link could do that, the HSRG did not comment.

Recent problems with regard to Northern Irish trade flows from Britain would not be affected by the construction of a tunnel, given that the issues relate to Northern Ireland's legal status in relation to the EU post-Brexit, rather than the physical makeup of its border with Britain.

Even a €20 billion engineering marvel would struggle to match the level of change that Brexit has brought to the islands.