A bridge across the Irish Sea "ought to be possible" and could be built within 15 years, according to a structural engineer and bridge designer.
Ian Firth, a fellow at the Institution of Civil Engineers, said there were a "huge number of technical challenges" in Boris Johnson's proposal to link Scotland and Northern Ireland.
But he said "anything is possible if you throw enough money at it" - and that such a structure could be built within 15 years.
"My own feeling is that it ought to be possible because at the end of the day it's about money - anything is possible if you throw enough money at it," Firth said.
"It has a huge number of technical challenges but that's what us engineers are in the business of solving.
"I'm a great believer in the possible."
He said very deep water, the risk of a ship hitting the bridge supports, and an underwater munitions dump in the sea could pose the biggest challenges to its construction, along with the economic and political hurdles.
However, he thought that the bridge could be designed within three years, subject to gathering the necessary data, and constructed within six years.
Additional time would be needed for environmental and geotechnical studies, Firth said, making it more likely to be completed within 15 years.
He 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".
Mr Firth suggested that submerging a tube and tethering it to the seabed could prove a simpler option.
