Speaking as he returned from a trip to the USA, the prime minister downgraded the plan to an “ambition”, which he acknowledged would not come to fruition until “substantially after” other infrastructure projects such as HS2.
His comments effectively sounded the death knell for a £20bn scheme that he previously insisted was realistic, despite being widely derided by engineers over the technical challenges and price.
Johnson first suggested connecting Stranraer in Scotland to Larne in Northern Ireland by a 28-mile bridge bridge three years ago to a chorus of scepticism from experts. Concerns were raised from the start about the practicality of spanning a stormy stretch of water more than 1,000 feet deep in some places, parts of which had been used as an offshore ammunition dump during the Second World War.
Experts said it would require dozens of support towers at heights never achieved anywhere in the world.
More recently, Johnson floated the alternative of a tunnel between Stranraer and Larne, while an even more ambitious proposal envisaged an underground hub beneath the Isle of Man with “spokes” connecting to sites in England, Scotland and Northern Ireland.
Mr Johnson has insisted the idea is serious, commissioning a feasibility study from a transport connectivity review led by Network Rail chair Sir Peter Hendy.
But the under-sea option was blasted as “the world’s most stupid tunnel” by former No 10 aide Dominic Cummings, and the Treasury let it be known earlier this month that chancellor Rishi Sunak had ruled it out from his October spending review on cost grounds.
Now Mr Johnson has effectively accepted that the bridge too is no longer an option for the foreseeable future.
Asked which of his grandiose infrastructure plans were ever likely to see the light of day, the PM indicated that he expects the eastern leg of the HS2 rail link from Birmingham to Leeds and beyond to go ahead, but was gloomier about the prospects for the Irish Sea link.
“You’ll have to wait til the spending review and the integrated rail plan, which is also coming out,” he told reporters.
“It will be wonderful for all parts of the north, northeast, northwest, Leeds, Derby, Newcastle, Liverpool, Manchester. We have wonderful plans.
“What I would say, perhaps, about the tunnel/bridge is perhaps, although it remains an ambition, it’s not the most immediate. It will be delivered substantially after the rest of the programme … just described.”
With even the first phase of HS2, linking Birmingham to London, not due for completion until between 2028-31, Mr Johnson’s comments indicate that he does not expect an Irish Sea bridge to go ahead during his time in office.
It is not yet known how much public money has been spent on considering the PM’s proposals for a fixed link crossing the Irish Sea.
An earlier plan for a garden bridge across the River Thames in London, vigorously promoted by Mr Johnson while the city’s mayor, was ditched in 2017 at a cost of £43m to the taxpayer.