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Vehicles arrive at Larne Port, in Northern Ireland, in a Nov. 14, 2018, file photo. The preferred location for a bridge connecting Scotland to Ireland is between Portpatrick, on Scotland’s west coast, and Larne, which is outside Belfast.Brian Lawless/The Associated Press

When British Prime Minister Boris Johnson mused about building a bridge between Scotland and Ireland, critics scoffed and called it another "Boris pipe dream.”

But the idea has been slowly gaining traction, and proponents say the prospect of driving from Dublin to London and on to Paris one day is no longer far-fetched. Indeed, Mr. Johnson reiterated his support for a bridge after he won last month’s general election and has instructed officials to look into the feasibility of the project. Irish Prime Minister Leo Varadkar has also voiced his support for a fixed link.

“I think it’s eminently doable,” said Glasgow architect Alan Dunlop, who has developed a bridge design. “I genuinely think that there is now a well of optimism and positivity coming from various people to suggest we should carry out a feasibility study.”

The dream of connecting Scotland to Ireland with a bridge or tunnel has been around for more than a century, but the plans never got very far. That’s largely because of the cost – at least $34-billion – and the engineering challenges.

The shortest distance over the Irish Sea is roughly 20 kilometres, from Torr Head on the north coast of Northern Ireland to the Mull of Kintyre in Scotland. But the highway network is better farther south, and the preferred location for a bridge is between Portpatrick, on Scotland’s west coast, and Larne, which is outside Belfast.

That bridge would span 41 kilometres, making it one of the longest waterway crossings in the world. It would also stretch over Beaufort’s Dyke, a trench along the Scottish coastline that’s five kilometres wide and 300 metres deep. The trench was a major disposal site for the British military after the Second World War; it was filled with 1.2 million tonnes of unused weapons, including canisters of mustard gas.

Proposed ‘Celtic Bridge’ would link Scotland and Northern Ireland

Detail

BRITAIN

IRELAND

London

Possible

routes

0

150

KM

Mull of Kintyre

Irish Sea

Cheaper but poor transportation links

Torr Head

Would cost at least £20-billion or $34-billion

SCOTLAND

Portpatrick

Larne

NORTHERN

IRELAND

Belfast

0

20

KM

How the bridge could look

Architect Alan Dunlop said the bridge would cost about £20-billion. Based on sketches provided by the architect, this is how the bridge could look

Up to 41 km

MURAT YÜKSELIR / THE GLOBE AND MAIL, SOURCE:

TILEZEN; OSM CONTRIBUTORS; ALAN DUNLOP; BBC

Proposed ‘Celtic Bridge’ would link Scotland and Northern Ireland

Possible

routes

Detail

BRITAIN

IRELAND

London

0

150

KM

Mull of Kintyre

Irish Sea

Cheaper but poor transportation links

Torr Head

Would cost at least £20-billion or $34-billion

SCOTLAND

NORTHERN

IRELAND

Portpatrick

Larne

Lough

Neagh

Belfast

0

20

KM

How the bridge could look

Architect Alan Dunlop said the bridge would cost about £20-billion. Based on sketches provided by the architect, this is how the bridge could look

Up to 41 km

MURAT YÜKSELIR / THE GLOBE AND MAIL, SOURCE: TILEZEN; OSM CONTRIBUTORS; ALAN DUNLOP; BBC

Proposed ‘Celtic Bridge’ would link Scotland and Northern Ireland

Glasgow

Possible

routes

Detail

Isle of

Arran

BRITAIN

IRELAND

London

Mull of Kintyre

0

150

Irish Sea

KM

Cheaper but poor transportation links

Torr Head

Would cost at least £20-billion or $34-billion

NORTHERN

IRELAND

SCOTLAND

Larne

Portpatrick

Lough

Neagh

Belfast

0

20

KM

How the bridge could look

Architect Alan Dunlop said the bridge would cost about £20-billion. Based on sketches provided by the architect, this is how the bridge could look

Up to 41 km

MURAT YÜKSELIR / THE GLOBE AND MAIL, SOURCE: TILEZEN; OSM CONTRIBUTORS; ALAN DUNLOP; BBC

Mr. Dunlop said the challenges can be overcome with new bridge technology. He has proposed a floating structure that would run along the top of the water and connect to pontoons and artificial islands anchored to the seabed by cables. The structure would be broken up by a suspension bridge to accommodate ships. Similar floating bridges are being used in Norway as part of the country’s massive coastal highway project, which stretches more than 1,000 kilometres and crosses several deep fjords.

Mr. Dunlop estimated the cost at about £20-billion, or $34-billion, and is convinced the money would be well spent. “There’s nothing like a bridge as a symbol of a forward-looking country,” he said.

He cited the success of the Oresund Bridge, a 16-kilometre road-rail link that connects Copenhagen to Malmo, Sweden. It opened in 2000 and replaced a one-hour ferry trip with a 10-minute train journey or short hop by car. The bridge cost about $7-billion and has generated more than twice that in economic returns, Mr. Dunlop said. He added that the ferry between Portpatrick and Larne takes about two hours and costs £300 a trip.

There are plenty of skeptics who question the economic viability of a bridge. While Larne is close to Belfast, the village of Portpatrick is more than 150 kilometres from Glasgow. An analysis by Esmond Birnie, an economist at Northern Ireland’s Ulster University, concluded that “even on the most generous assumptions it is unlikely that the total measurable economic benefits of such a bridge would come anywhere close to its very considerable cost.”

Another complication is Britain’s pending departure from the European Union. Mr. Varadkar says that if the bridge runs from Scotland to Northern Ireland, the United Kingdom will have to pay for it with no help from the EU. It may also have to include customs checks, since Northern Ireland will remain tied to the EU’s regulations under Britain’s withdrawal agreement with the bloc.

There are also tricky political considerations. Northern Ireland’s Democratic Unionist Party strongly favours a bridge because it would strengthen the province’s connection to the U.K. However, Sinn Fein and other parties that favour closer ties with Ireland oppose the project. And while the bridge has support in Scotland, there’s the question of what would happen to it if Scotland were to vote for independence.

Scottish First Minister Nicola Sturgeon, who heads the Scottish National Party, has also questioned Mr. Johnson’s commitment. The Prime Minister “has a track record of promising big projects like that and he has no idea how to deliver, ultimately does not deliver,” she said recently.

Mr. Dunlop isn’t deterred. He noted that Prince Edward Island spent decades debating the merits of a fixed link with New Brunswick before the Confederation Bridge opened in 1997.

“There will always be naysayers and people who will pooh-pooh the whole prospect of the thing,” he said. “But I think that in 30 or 40 years’ time, there will be a bridge connecting Scotland over to Ireland.”

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