A land bridge or tunnell between Ireland and Scotland is once more back in the public debate.The idea of a permanent land link between Ireland and Britain and indeed Europe, has been arond for some time.

At its closest point the land masses are only 12 mies away but the part of Scotland near the Mull of Kintyre is very remote.

The ppprincipal proposal is a 21 mile bridge, one of the longest in the word, secnd only to a 22 mies bridge over water in Asia.

Ireland and Scotland share many things: beautiful countryside, similar native languages, highly-rated accents, and even the Irish “craic” was originally a Scottish word. So why not a Celtic connection bridge too?

Taking a trip over a bridge, watching Scotland slowly come into view before you may sound idyllic, but after decades of debate is there now a realistic chance?

Supporters of such an endeavor claim that a tunnel or bridge would be beneficial for tourists in both countries, those against such a proposal believe that the enormous initial spending involved would make the project prohibitively expensive.

Engineers and politicians on both sides of the Irish Sea have long been fascinated with the idea, but it seems that each prospective plan faces many obstacles.

Ireland and Scotland are already easily linked by ferry and, of course, by plane. It is generally believed that such a tunnel could not live up to the success of the Channel Tunnel between Southern England and France. The Eurotunnel continues to grow its traffic numbers on an annual basis, last year 21 million passed through it.

Read more: Is “Craic” a fake Irish word?

The debate continues, however, and last year Northern Ireland politician Sammy Wilson called for a feasibility study on the subject of building a similar passage between Northern Ireland and Scotland, calling it a "visionary idea" that would act as a solution to the high cost of ferry travel and ferry cancellations due to poor weather conditions.

Similar studies have already been carried out including one completed as recently as 2007 by the Center for Cross Border Studies. They estimated that a bridge from Galloway in Scotland to Ulster would cost up to £3.5 billion ($5.1 billion), a hefty sum when there still remains some uncertainty over whether it would be heavily used. A tunnel would cost much more.

The group asserts, however, that such a bridge (or tunnel) would greatly boost intercity rail travel, with passengers able to step on a train in Glasgow or Edinburgh and alight again in Belfast or Dublin.

“It struck me that the gains to be obtained from building a bridge which might cost a couple of billion across the North Channel between Scotland and Ireland would outweigh the cost,” said Andy Pollack, director of the group when the report was published.

There are four main routes that have been highlighted as possibilities for connecting Ireland and Britain. Two stretch between Northern Ireland and Scotland, while the remaining two would bring passengers from the Republic of Ireland to Wales. Another suggestion has been to build two bridges on either side of the Isle of Man, but the idea of building two such long-distance bridges is thought to be extreme.

Read more: Amazing woman attempts to run across the Irish Sea in a big inflatable barrel

In Northern Ireland, a 12-mile passage could be established between Antrim and the Mull of Kintyre, or a 21-mile passage between Portpatrick and Belfast Lough. Although on face value it may seem easier to pick the 12-mile option, the Mull of Kintyre route would involve further travel over water and heavy upgrading on transport systems through mountainous terrain on either side. As such, it would be the more expensive option.

Routes between the two countries via the North Channel also face the problem of Beaufort’s Dyke, a 31-mile long, 650-foot deep sea trench that was used as a dumping ground for conventional and chemical munitions in the aftermath of the Second World War. The Dyke has been a constant set-back for those suggesting a Ireland-Scotland passage since the the idea first began floating around in the 19th century.

Though such long-distance bridges are used in other areas of the world, the case for an Ireland-UK bridge has been deemed impractical due to the depth of the water between Ireland and Scotland, as well as the weather conditions across the North Channel.

“The North Channel is something like 32,000 metres (105,000 feet) coast-to-coast, whereas the Forth Road Bridge is around 2,500 metres (8,200 feet) in comparison,” Ronnie Hunter of the Scottish Institution Of Civil Engineers told The Scotsman.

“If you’re talking about building a bridge, it would be multi-span and require dozens of piers across the channel.

“There are numerous bridges in North America built across relatively shallow water which go on as causeways for mile after mile. But we’re not talking about shallow water here – this is essentially next to the Atlantic Ocean, in very deep water.”

The bridge would certainly give #Scotland and Northern Ireland and a welcome tourism boost! #UK2NIBridge #FridayFact pic.twitter.com/GqTZLRm9AI — Cleveland Bridge UK (@CleveBridgeUK) April 1, 2016

He adds that the cost of a tunnel makes that seem unlikely.

“The length suits a tunnel,” he said. “It would likely have to be a rail tunnel, rather than a road tunnel, as it is hard to get the ventilation right.

“One slight problem, which could easily be overcome, is that track gauge is different in Ireland to the UK.

“But what you have to ask yourself is, is there a benefit in building such a link? Someone is going to have to face a substantial cost, and it’s not clear to me you could make that cost-benefit calculation work.

"The distance is not far off the Channel Tunnel but there isn't the soft rock, the chalk and sandstone. It would be a stretch but doable. The issue is the cost to the Treasury based on any cost benefit, not the political will. Who would underwrite such a project?"

I don't know if I would vote DUP in Northern Ireland, but their idea for a bridge/tunnel from N.I to Scotland is really interesting ! ���� — Dylan (@dmcd696) April 21, 2015

With the UK possibly on the verge of leaving the EU, could this cause further problems for Irish tourists dreaming of a day-trip in Scotland, with so little government support already shown for the suggestion?

While recognizing the importance of an easy link between the two countries, many politicians feel that greater investment should be placed in the current tested and proven systems of transportation, such as the ferry.

“We very much welcome the investment that both P&O and Stena [ferry service companies in Britain] have made improving the ports and vessels on the ferry routes from Loch Ryan to Larne and Belfast in recent years,” said a spokesperson for the Scottish Government.

“We are supporting this through the continuing maintenance of the trunk road network to allow people to reach the port safely and efficiently with £58 million invested in the M77 and A77 since 2007.”

Someone build a bridge from Scotland to Ireland 'cause we're clearly the best two countries here — jonj (@JonjoBrannen) May 23, 2015

#3 Or we could slide the top to form a bridge to Ireland & a better rain shield for Glasgow#Scotland pic.twitter.com/yLYt1NENmp — Elon Dann (@ElonDann) May 17, 2016

H/T: The Scotsman