Engineering experts have poured cold water over UK Prime Minister Boris Johnson’s plan to build a bridge between Scotland and Northern Ireland for £15 billion (US$18.5 billion).
Johnson – who first touted the idea of the 35km bridge last year – put a price on his proposal for the first time last week, saying it would “only” cost the multibillion pound sum.
But experts have said that, while it might technically be possible to construct the bridge connecting Scotland’s mainland with the outskirts of Belfast, it is potentially fraught with problems and the costs could spiral.
One eminent engineer, who was behind London’s Millennium bridge, said it was “bonkers” to put a price on the plan before a proper design was in place. Another engineering academic labelled the proposal “dubious economics”.
It comes after leaked documents emerged on Tuesday that revealed that Johnson had ordered government officials to explore the possibility of building the bridge.
On Thursday, during a visit, the prime minister told schoolchildren : “[I was talking yesterday] about building a bridge from Stranraer in Scotland to Larne in Northern Ireland – that would be very good. It would only cost about £15 billion”.
Johnson first floated the idea in an interview last year, saying: “What we need to do is build a bridge between our islands. Why don’t we? Why don’t we?”
But his proposal drew criticism then, with one retired engineer comparing the feasibility of the plan to “building a bridge to the moon”.
James Duncan, from Edinburgh, raised concerns over the practicality of constructing a bridge across the “stormy” stretch of water – more than 300 metres deep in places – which would require dozens of support towers at heights “never achieved anywhere in the world”.
Bridge builders would also have to navigate Beaufort’s Dyke, a submarine trench in which the UK Ministry of Defence dumped more than 1 million tonnes of obsolete munitions following the end of the World War II.
Chris Wise, the engineering designer of the 2012 Olympic velodrome, said he supported the principle of connecting the two countries but raised a series of question marks over the practicality of the proposal.
“It’s socially admirable but technically clueless,” he said.
“If Boris wants to stay prime minister he needs to stop promising figures before he can deliver them.”
Wise, the engineering director behind London’s Millennium bridge, explained: “Technically, there’s a solution which is to build something in dry dock, tow it out, sink it into position. But when you’re talking about something that is going to be the same height as the Eiffel Tower before you even get to sea level that’s a major, major beast.
“It probably means you’re not going to be putting any supports in there [to hold up the bridge] so then the question is whether the span you’re left with is something that is plausible. Because the biggest bridges in the world are only a mile, or a mile and a bit long for an individual span [without a support].”
Similar bridges have a series supports to hold the structure in place. They include the 7.8km Oresund bridge, which connects Sweden to Denmark.
The idea of a bridge across the sea was explored in the 19th century, and former Conservative prime minister Margaret Thatcher’s government examined plans for a road crossing in the 1980s.
Northern Ireland’s Democratic Unionist Party, which has close ties to Johnson’s Conservatives, has supported the idea of a bridge since at least 2015.
A UK government spokeswoman said: “The prime minister has often spoken about his support for infrastructure projects that increase connectivity for people and particularly those that strengthen the union. As you’d expect, the government regularly commissions work to examine the feasibility of potential projects.”