A proposed mega-project that would bring UK and America closer together via an incredible tunnel would cost an eye-watering £15.6trillion – which is just one of the reasons it is unlikely ever to go ahead.

The Transatlantic Tunnel is an idea that has been around for more than a century and is pretty much exactly what it says on the tin, a tunnel under the Atlantic Ocean connecting the UK and North America.

This monstrous project would stretch for 3,400 miles under an ocean which in some areas…