Boris Johnson’s proposal to link Scotland and Northern Ireland with a bridge is not only “possible” –but could be built within 15 years, according to a structural engineer.
Ian Firth, a fellow at the Institution of Civil Engineers, said there were a "huge number of technical challenges" in the prime minister’s idea for a crossing between the two areas across the Irish Sea.
But the bridge designer said "anything is possible if you throw enough money at it" – and that such a structure could be built within 15 years.
The proposal of a bridge over the 20-mile gap between Northern Ireland and Scotland has been modelled on the Öresund Bridge, which runs for five miles across the Öresund strait between Sweden and Denmark.
One idea for the bridge that Firth suggests is a cable-supported floating bridge with towers supported by large, submerged pontoons connected to the sea bed by cables.
A bridge above the water faces the potential issue of ships hitting bridge supports, so they would need to be spaced by about 1km apart, meaning no more than two ships could pass at any one time.
A potential solution to this could be to not have a bridge at all, and instead submerging a tube and tethering it to the seabed, Firth saidFirth.
However, a tunnel could limit safety options in the event of a fire or an accident, according to The Conversation.
Firth described the project as being "right up there" with the toughest bridges built thus far in the world, and said he thought such a plan would be "eye-wateringly expensive”.
Chris Richards, head of policy and public affairs at the Institution of Civil Engineers, said the proposal should be put to the National Infrastructure Commission and subject to a "comprehensive and independent" study.
Downing Street said this week that a "range of officials" were looking at the idea of a bridge, but was unable to say how many civil servants were examining proposals.
The prime minister's official spokesman said it was a "proper piece of work" and that Johnson was "ambitious" about infrastructure projects across the country.
Johnson has repeatedly spoken about such a bridge, even though experts have warned that the depth of the Irish Sea and the presence of dumped munitions would cause problems for any project.
The project could cost a reported £20bn, although Johnson has previously said it would "only cost about £15bn”.
The prime minister told MPs "watch this space" when asked about the prospect of a "Boris bridge" in Parliament in December 2019.
The distance from Larne to Portpatrick, one of the most likely routes for a bridge, is around 45km.
There is no problem with distance, money or the Beaufort's Dyke explosives disposal area, according to the prime minister.
Government sources said it was possible to build a bridge with a tunnelled section to cope with some of the difficulties caused by the depth of the Irish Sea.