BORIS Johnson has been ridiculed after calling a for a bridge between France and England.

The Foreign Secretary reportedly made the unexpected proposal on Thursday night while Theresa May and French President Emmanuel Macron were meeting in Sandhurst.

He told Macron that it was ”crazy that two of the biggest economies in the world are connected by one railway line when they are only 20 miles apart”.

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It’s not clear if May knew her Foreign Secretary was going to come out with the suggestion for a new bridge.

But Downing Street yesterday dismissed the calls.

As too did almost anyone with knowledge of the English Channel, engineering, infrastructure, and what already exists.

“Building a huge concrete structure in the middle of the world’s busiest shipping lane might come with some challenges,” the UK Chamber of Shipping tweeted.

The Chamber’s chief executive, Guy Platten, later explained: “It’s good to have vision, particularly with respect to transport infrastructure projects, but the Dover Strait is the world’s busiest shipping lane. Many, many hundreds of vessel transits are made each day by commercial shipping, fishing and pleasure craft.

“Building a 22-mile-long bridge across the Channel would be a huge construction project, especially as the largest ships currently transiting the strait have a height above the water line in excess of 70 metres.”

May’s spokesman was put on the spot about the proposal repeatedly during his briefing with journalists.

He said: “I have not seen any plans on that but what I would say is we are going to have very close ties with France economically, culturally and in areas like defence and security for many many decades to come.

“What was agreed yesterday, and what the Foreign Secretary tweeted about as well, is a panel of experts who will look at major projects together, including infrastructure, and we want to work very closely with our French colleagues on building a shared, prosperous future.”

Asked if the panel of experts would look at the “Boris bridge” proposal the spokesman said: “As I have said I have not seen any plans for that.”

When asked if Johnson had told May about his idea, he replied: “I have not seen any plans for that...”

Asked if May thought the idea was good in principle, the spokesman said: “I have not seen any plans for a bridge.”

Asked if the Foreign Secretary’s idea had come as a surprise to the Prime Minister, the spokesman added: “Look, the Foreign Secretary set out in his tweet, something which was set out more formally on this panel of experts to look at major projects together and that’s something we support.”

He added that the Prime Minister thought Johnson was doing an “excellent job”.

While engineers said it wasn’t impossible, it would require cutting a fair amount of corners to make the cost feasible.

The 1.7mile Queensferry Crossing, which opened last year, cost £1.3 billion.

Architecture lecturer Alan Dunlop, said he’d imagine the Boris Bridge would cost £120bn.

He dismissed those pointing out that the new 34-mile sea bridge linking Hong Kong and Macau, only cost £12bn.

“That’s without any regulation, processes, health and safety and using Chinese workers,” he told the Times. “I’d say at least £120bn for a Channel bridge and that’s a conservative estimate. It would really be cheaper to move France closer.”

Emily Thornberry, the Shadow Foreign Secretary, tweeted: “I ignored this earlier because I assumed it wasn’t real. Apparently it is. I mean ... who are these clowns claiming to run our country?”

The SNP’s Foreign Affairs spokesman, Stephen Gethins, whose North East Fife constituency stops at the Tay Bridge, said: “Leaving the EU will be devastating for jobs, the economy and opportunities for young people. Part of the reason we are in this mess is because Boris Johnson and other senior government figures campaigned without having the decency to tell voters what their plans were.

“This latest wheeze demonstrates how little of a clue the Foreign Secretary has.”