Tunnel link in Irish Sea ‘£16bn less’ than bridge

A tunnel between Northern Ireland and Scotland could cost the taxpayer up to £16 billion less than a bridge, according to the architect whose plans for a crossing were backed by Boris Johnson.

Alan Dunlop, who first proposed a bridge across the Irish Sea in January 2018 and subsequently won the support of the prime minister, has now produced a design for a submarine tunnel that would be moored 12 metres below the waves and tethered to giant pontoons.

His latest scheme was partly inspired by the £36 billion Norwegian Coastal Highway, sections of which cross fjords 500 metres deep using concrete tubes.

His idea would also feature artificial islands off the coast, much like the £4 billion Oresund bridge and tunnel between Copenhagen and Malmo that opened in 2000. He went back to the drawing board after Alister Jack, the Scotland secretary, told MSPs this month that a crossing was being seriously considered by the UK government. However, Mr Jack added that Mr Johnson’s suggestion of a bridge was in fact a “euphemism” for a tunnel. “It would be less expensive,” he said.

Mr Dunlop has reached the same conclusion and estimates that a submerged tunnel would cost between £8 billion and £10 billion and take seven to ten years to build. He calculated that the price of constructing a 26-mile bridge between Portpatrick and Larne would be up to £20 billion, and that an alternative linking Glasgow directly with Ulster would cost up to £24 billion.

“A tunnel would require some sophisticated engineering, but it’s not the massive structure a bridge would have to be,” he said. “I’m absolutely convinced it can be done. It might seem mind-blowing but the Norwegians have shown such submerged tunnels are workable and safe.”

Harry Dimitriou, the Bartlett professor of planning studies at University College London and an expert on large infrastructure projects, said that there were “fundamental strategic questions over the need and benefit of a crossing”.

“There is a danger of over-focusing on the engineering and technical challenges,” he said. “The quoted figures are only ball-park costs and the price typically escalates when such a mega-project begins: just look at HS2 [the high-speed rail link]. ”

For now Mr Dunlop agrees that he might have to wait until a bridge or tunnel becomes politically fashionable again. Despite producing the first feasibility study over two years ago, he’s still waiting to be asked for further information by civil servants. “Boris has other things on his mind at the moment,” he said. “But I’ll keep pursuing it.”