Northern Ireland bridge or tunnel to Scotland would have cost at least £209bn

Some experts estimated a bridge could cost £20bn

A feasibility study of a bridge or tunnel from Northern Ireland to Scotland has concluded that it would be technically possible, but would cost a minimum of £209bn.

Sir Peter Hendy, who oversaw the review, said a link would have "transformational" economic effects.

However, he added that the costs would be impossible to justify.

Therefore he said further work on the link should not progress beyond the feasibility study.

The idea of a tunnel was first suggested more than 150 years ago.

Sir Peter said the study is the first "comprehensive, conclusive" examination of the technical issues.

The review said a bridge crossing would be the longest span built to date and a tunnel would be the longest undersea tunnel ever built.

Safety considerations mean that a tunnel crossing could only be constructed for railway use.

A combination of tunnel and bridge incorporating artificial islands, as employed in Scandinavia and China, would not be possible due to the depth of the Irish Sea and other inhibiting factors.

The indicative cost estimate for the full route, including optimism bias, is £335bn for a bridge crossing and £209bn for a tunnel crossing.

The authors said it was also important to note that the road and rail infrastructure required to connect a crossing to the main transport networks in Northern Ireland and Great Britain were, in themselves, major construction works.

The planning, design, parliamentary and legal processes, and construction would take nearly 30 years before the crossing could become operational.

The study also considered the carbon footprint of a link.

An upgrade to the A75 in Scotland would better connect NI cargo and freight to England, Grant Shapps said

It estimated that if the crossing replaced a reasonable proportion of flights between Great Britain and the island of Ireland with lower carbon intensity transport like rail, then the carbon cost of a bridge crossing would be offset in approximately 42 to 61 years, and a tunnel in 15 to 24 years.

Meanwhile, a Union Connectivity Review, which has examined transport investments, was published by the government on Friday.

UK Transport Secretary Grant Shapps has said a proposed upgrade to the A75 road in Scotland would be "very good news" for Northern Ireland.

The A75 is a key route for freight and cargo linking Stranraer and Cairnryan ports with the English border.

"It largely links Northern Ireland and Scotland through to England, so it's very important in terms of a trade route, a cargo route, a freight route," Mr Shapps told Good Morning Ulster.

The transport secretary said it was important the government was taking an "overview" of infrastructure needs across the UK for both the movement of goods and people.

'Cost and complexity'

Asked about the plans to build a bridge, Mr Shapps said it was "absolutely right" to look at the issue.

"As it so happens, this review now rules that out on the basis of cost and complexity," the secretary of state explained.

In September, Northern Ireland's Infrastructure Minister Nichola Mallon had said the plans had been "put to bed" and described the bridge as a "distraction" and a Conservative Party "vanity" project.

Mr Shapps responded that he would "encourage her to turn down that kind of rhetoric".

"I prefer not to play politics with this, I think we need to improve all our connections," he continued.