• Boris Johnson said his plan to build a bridge connecting Northern Ireland to Scotland would “only cost about £15 billion.”
  • The prime minister has reportedly asked UK government officials to assess the pros and cons of constructing a bridge across the Irish sea.
  • One engineering expert branded the proposal a “thoughtless soundbite” that “no sane contractor or responsible government” would sanction.
  • Visit Business Insider’s homepage for more stories.

Boris Johnson has said his plan to build a bridge from Northern Ireland to Scotland after the United Kingdom leaves the European Union “would only cost about £15 billion.”

The prime minister on Thursday told schoolchildren his “very good” idea of constructing a bridge connecting Scotland to Northern Ireland would cost approximately £15 billion ($18.5 billion.)

Johnson has asked officials in his UK government to look at the costs and risks of building a 28-mile bridge across the Irish Sea.

Read more: Fuel shortages, bankrupted businesses, and riots: Official UK government document forecasts no-deal Brexit chaos

The prime minister has reportedly asked officials to examine "where this money could come from" as well as "the risks around the project," one of which appears to be unexploded bombs dropped into the sea during World War II.

Speaking to schoolchildren in central London today, Johnson said: "[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 reportedly believes a bridge connecting Nothern Ireland with Great Britain could help shore up relations within the UK amid growing divide over Brexit.

Both Northern Ireland and Scotland voted to stay in the EU, and the former is facing the prospect of a hard border with the Republic of Ireland, which would harm businesses there and potentially trigger civil unrest.

The prime minister first suggested the idea of a bridge across the Irish Sea when he was foreign secretary in 2018 and has apparently revived it since entering Downing Street.

His proposal was, at the time, branded by one expert as a "thoughtless soundbite" that "no sane contractor or responsible government" would sanction.

Writing to The Sunday Times last year, James Duncan, a retired offshore engineer from Edinburgh, said the idea was "about as feasible as building a bridge to the moon."

"Many long bridges have been built, but none across such a wide, deep and stormy stretch of water," he continued.

"For a great part of the 22-mile route the water is more than 1,000 feet deep. It would require about 30 support towers at least 1,400 feet high to carry the road deck across the deepest part and above the shipping channel. In total the bridge would require 54 towers, of heights never achieved anywhere in the world."