The cost of the bridge caused concern among UK officials, who asked the prime minister to use this money to improve infrastructure in both countries instead.

Boris Johnson’s idea to build a bridge between Northern Ireland and Scotland could transform into a tunnel in the Irish Sea, said Scotland’s Secretary of State Alister Jack. Addressing members of the Scottish Parliament, he noted that the tunnel would avoid the issue of Beaufort’s Dyke. Jack also said that the idea of a bridge is a euphemism for a link between Edinburgh and Belfast.

Downing Street recently acknowledged that experts are reviewing the PM’s proposal to see whether it is viable. Johnson first voiced the idea of building a 20-billion pound bridge between Northern Ireland and Scotland during the Conservative Party leadership contest in the summer of 2019. It received support from the unionists in Belfast.

But the idea was harshly criticised by Scotland, other UK politicians, and engineers, who dismissed it as clueless and bonkers. Experts said although the idea is feasible its implementation will run into problems, which will dramatically increase its cost. One of the main issues is Beaufort’s Dyke, a trench containing thousands of Second World War munitions.

Alister Jack said that a tunnel from Scotland’s Portpatrick to Larne in Northern Ireland will deal with the issue of Beaufort’s Dyke. "It’s no different to the tunnels connecting the Faroes, it’s not different to the tunnels underneath the fjords”, he said. Jack noted that the prime minister was "on the same page" with him on the idea of a tunnel.

Still many in the UK oppose the idea. After it was announced that the estimated cost of the bridge would be 20 billion pounds ($25 billion) transport secretaries in Scotland and Northern Ireland wrote a letter to PM Johnson asking him to split the money between the two countries in order to improve their infrastructure.