When it comes to the old adage of "if at first you don't succeed, try and try again" it appears Boris Johnson is a firm believer.
Hoping to be the prime minister who transforms the UK's infrastructure, one of his favourite ideas is a bridge from Scotland to Northern Ireland spanning across the Irish Sea.
He keeps bringing the idea back, despite his first proposal being too short to cross the sea and his second running right across Beaufort's Dyke, the UK's largest dumping ground for munitions and chemical weapons from the Second World War.
Johnson recently raised the suggestion of a bridge over the Irish Sea once more, so will he ever get it built?
The Claim
Every time Johnson brings up his plans for a bridge between Scotland and Northern Ireland a host of engineers and experts line up to point out what a ridiculous suggestion it is. Retired offshore engineer James Duncan suggested a bridge over the Irish Sea would be “about as feasible as building a bridge to the moon”.
Some have criticised the economic projections for the bridge as unrealistic, while others warn that building a bridge across an often stormy sea would be a difficult task no matter how much money was available.
To build a miles long bridge across the sea is no easy feat and the support columns for it would have to stand in water over 1,000ft deep in places. Supports for the bridge would have to be the largest ever created in the world.
The shortest possible route would have to cross Beaufort's Dyke, meaning the bridge must either be built among unexploded bombs or it must be built elsewhere and be much longer.
All in all, the idea of building a bridge over the Irish Sea keeps being shot down as expensive and improbable, while constructing it over a trench filled with a million tonnes of unused munitions is likely to cause concern at various stages.
The Counter Claim
That's not to say Johnson's grand plan doesn't have some support from other political figures. Irish Taoiseach Leo Varadkar thinks the bridge is worthy of consideration and hopes a review will take it seriously.
Both he and Johnson appear to be taking the project seriously and the British prime minister told the House of Commons to "watch this space" on the potential for a bridge.
However, why does it need to be a bridge? Johnson once had an idea for a bridge across the English Channel which was also shot down almost immediately, but the Channel Tunnel has been open and incredibly successful for years.
An Irish Sea tunnel wouldn't be subject to the whims of stormy weather and wouldn't need the world's largest support towers to keep it up either. It could also be built elsewhere and go around Beaufort's Dyke, as the prospect of going under a trench full of bombs is still about as appealing as going over it.
Bill Grose, former chairman of the British Tunneling Society and lead author of a report from the Institution of Civil Engineers, argued that the tunnel would cost roughly the same as a bridge and could run from somewhere north of Liverpool through the Isle of Man and towards Belfast.
That would put the tunnel in England rather than Scotland, with the starting point somewhere near Workington.
The Facts
Modern tunneling machines are three times as fast as those that dug the Channel Tunnel in the 90s and could become even faster by the end of the decade, making digging a tunnel many miles long more feasible.
For point of reference the Channel Tunnel is 31 miles long and took six years to dig. Faster tunneling technology means an Irish Sea tunnel could be completed in a similar time scale despite being much longer.
A tunnel would have to be much longer than the original plan for the bridge, with the proposed route from Grose requiring 84 miles of tunnels to be dug beneath the Irish Sea.
The shortest route would go from the tip of Scotland's Mull of Kintyre to the coast of Northern Ireland's County Antrim and take just 12 miles, but the areas around the tunnel entry points lack ports and roads to get there.
A tunnel people can't get to which drops them in the middle of nowhere isn't going to bring the hoped for economic benefits.
Going around Beaufort’s Dyke is crucial as the Ministry of Defence estimates that there are around 1.5 million tonnes of munitions dumped there and there aren’t any maps of the exact locations of the weapons.
It currently costs around £80 million to build each mile of a twin rail tunnel and the areas around the entry points would also need extra development to deal with becoming a new transport hub.
While Johnson has repeatedly championed the idea of a bridge over the Irish Sea he might have better luck pushing for construction of a tunnel under it.
