Documents seen by Channel 4 News reveal that the Treasury and Department for Transport have been asked for advice on possible costs and risks.

Boris Johnson has told government officials to explore the possibility of building a bridge between Scotland and Northern Ireland.

Documents seen by Channel 4 News reveal that both the Treasury and Department for Transport have been asked for advice on the costs and risks of such a project.

The prime minister wants to know “where this money could come from” and “the risks around the project” – which appear to include “WW2 munitions in the Irish Sea”.

The idea was mooted by Mr Johnson last year, when he was Foreign Secretary.

The Department for Transport produced a “factual paper on the subject” after conversations between the DUP and former Secretary of State Chris Grayling — who himself presided over a number of controversial infrastructure schemes.

The DUP, the party supporting the Conservatives in Parliament, believes a bridge could break the Brexit impasse by removing the need for a border in the Irish Sea.

Government spokesperson told Channel 4 News: “Government regularly commissions work to examine the feasibility of projects. During the leadership campaign candidates spoke about a number of issues which resulted in Number 10 commissions ahead of a new Prime Minister taking over. This PM has made no secret of his support for infrastructure projects that increase connectivity for people and particularly those that strengthen the Union.”

Not the first bridge proposal

Boris Johnson is no stranger to an ambitious building project.

While Mayor of London, he threw his weight behind Joanna Lumley’s campaign for a “Garden Bridge” to straddle the Thames. But the plan was fraught with problems from the get-go, and saw Mr Johnson jetting round the world to raise cash for the project.

By 2017, the planned “floating garden” was in jeopardy, with the trustees in charge of overseeing construction warning that it was likely to “substantially exceed” the expected budget of £185 million.

It was eventually wound up that summer by Mr Johnson’s successor, Sadiq Khan, after a damning review by Labour peer Dame Margaret Hodge concluded “decisions on the Garden Bridge were driven by electoral cycles rather than value for money”. All-in, the failed project racked up a total cost to the taxpayer of £43 million.

But his City Hall ambitions didn’t end there. In 2011, the then-Mayor backed a plan for a Thames Estuary airport – quickly dubbed “Boris Island”.

Yet, like the Garden Bridge, the proposal never got off the ground. In 2014, the Airports Commission announced it would not include the proposed estuary site to its shortlist of candidates for airport expansion.

That didn’t stop Mr Johnson attempting to revive the scheme in 2016, during his final days as Mayor. Although he seemed to finally jettison the idea in this year’s Conservative leadership contest, when a spokesman for his campaign confirmed “plans for a Thames Estuary Airport are off the agenda”.

As recently as 2018, Mr Johnson hinted at the idea of another ambitious bridge when he was Foresign Secretary under Theresa May – but this time between the UK and France.

That idea itself is nothing new, and was even explored by the Victorians. More recently, Margaret Thatcher’s government interrogated plans for a road crossing for cars and lorries in the 1980s.

As Channel 4 News’ FactCheck team reported last year, experts consider a bridge connecting Britain to the continent to be a “huge undertaking” but “absolutely possible” thanks to modern technology. But expensive and challenging all the same.