The Prime Minister tempered expectations about his proposal for a bridge or tunnel in September, telling reporters that while it remained an “ambition”, it was not “the most immediate” priority.

Sir Peter’s report, A Fixed Line Between Great Britain and Northern Ireland: Technical Feasibility, considered the challenges of building a fixed crossing across the Irish Sea or North Channel via a tunnel, bridge or combination solution and identified the most viable solutions using current construction technology.

It found that both a tunnel and bridge option are “technically feasible to construct, maintain and operate a fixed link crossing between Great Britain and Northern Ireland”.

Sir Peter added that while future transport technological advances, such as autonomous vehicles, could allow for different tunnel and bridge designs, which could enable the construction of a fixed line at a lower cost, “the benefits could not possibly outweigh the costs to the public purse”.

The proposed route would have crossed water that runs more than 1,000 ft deep in places, which would have required some of the largest support towers ever constructed. The area was also used as an offshore ammunition dump in the Second World War, which threw up additional problems.

Strong gales across the body of water also raised the prospect that the bridge would frequently be forced to close.

Sir Peter added: “Despite my recommendation, I am clear that this was an excellent question to ask.”