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The Ulster - Scots call it the Narrow Sea. At its closest point, there are just 12 miles between Northern Ireland and Scotland. Community and trade links between the two countries stretch back centuries.

Now Boris Johnson – the PM who loves making model buses and is fascinated by large-scale infrastructure projects – wants to physically link these two parts of his disunited kingdom in order to demonstrate his commitment to the Union. His first thought was a bridge, but this has 'morphed' into the idea of a tunnel and now he has commissioned a feasibility study under the auspices of Sir Peter Hendy, Network Rail Chairman. It's due to report later this year.

Not surprisingly, Ulster Unionists would love it, but nationalists in Northern Ireland and Scotland dismiss it as nothing more than a 'Boris vanity project' and there's similar scepticism among the major political parties.

It's not a new idea – proposals to build bridges and tunnels, under the Irish Sea, date back to the 1870s. Away from the politics, some civil engineers and architects agree that it is feasible but only at a huge cost and Herculean effort to overcome the engineering difficulties of working in this turbulent stretch of water with the notorious Beaufort Dyke trench, where thousands of tonnes of munitions were dumped after World War Two. The projected price of 'Boris's Burrow' is somewhere between £15-20 billion. Some economists argue a tunnel would increase trading opportunities throughout the UK, others that such benefits are impossible to predict.

At a time when the UK's constitutional future is fast becoming a major issue, Mark Simpson will 'stress test' the merits and criticisms of Boris's plan and ask is it just a pipe dream or could it conceivably be built?