A bridge from Scotland to Northern Ireland? Boris Johnson’s proposal to link the two countries with a road crossing over the Irish Sea would, most experts agree, cost a lot more than the £15 billion he is suggesting. And the engineering involved would be more than a little complicated. But is it technically possible?

Yes, according to several experienced bridge engineers and designers. Alan Dunlop is a Scottish architect who, in 2018, was commissioned by a newspaper to analyse the feasibility of such a project. He suggested two routes: a 12-mile crossing that spans the shortest gap between the two countries – Mull of Kintyre in Scotland to Torr Head, Northern Ireland. And, to the south, a 26-mile crossing from Portpatrick to Larne. The northern route is unlikely since the ports in question are more remote, and the road improvements needed might end up costing as much as the actual bridge. The southern route, which would be closer to Belfast and Scotland’s Central Belt is more practical, given the existing road infrastructure on both sides.