IN A back lane of Moscow a few hundred yards from the Kremlin, an offset Nordic cross hangs outside a pastel yellow townhouse.

The flag marks the latest embassy, or rather representation office, of archipelago with a population smaller than Kirkcaldy. But big diplomacy happens here, giant trade deals bypassing Western sanctions on Russia after its annexation of Ukraine’s Crimea. This is where the tiny Faroes talk fish.

As Brexit looms, Britain will “take back control” of fisheries from the EU. Aside from the many enthusiastic trawler skippers and Eurosceptic tabloids few in Scotland have given this much thought. But we should. Because the move, if fisheries are fully devolved, will thrust this country in to the world of geopolitical intrigue like nothing else since Darien.

Fish is big. Fish is very big. Take the wee Faroes. Officially outside the EU but still part of Denmark, they have devolved powers over their fisheries, which account for 95 per cent of their exports. That means they have to have a foreign policy. They have to enter in to bilateral relations with Brussels and with other major fishing states, such as Russia, Iceland and Norway, over who gets access to their waters. This means they can please their neighbours and it means they can peeve them.

When the islands opened their little office in Moscow back in 2015 Russia had just been hit by hefty sanctions from the EU and other countries. These, inevitably, affected the world’s most traded foodstuff: fish. Russia hit back with a ban on the import on salmon from the EU, including Scotland. Our fishers faced a slump as a result. Not the Faroes. They struck a deal to sell more of their pink stuff to Russia, their biggest export market.

It is worth labouring this point: the Faroes has effectively pursued a different policy on Russia than Denmark and the rest of Nato and the EU. Most significantly devolved sub-states – as the jargon goes – have overseas interests that differ slightly than those of their metropolitan. Scotland is no exception with a network of offices around the world protecting and promoting its case on key devolved issues like economic development. But fishing puts this on a whole new level, as recent history illustrates.

In the difficult years when Britain was trying and failing to join the then common market, the country fell out with one of its neighbours, Iceland, over fish. The country had imposed a 200-mile exclusive economic zone. Scottish and English fishers were not allowed to trawl these waters, their traditional catching grounds. Cue what became the Cod Wars, two lengthy confrontations involving the Royal Navy. An Icelandic Coastguard engineer died when his boat collided with a British one. But the dispute, only resolved when the UK finally got into Europe in 1973, showed just how fishing can colour diplomatic relations.

At one point Iceland, strategically crucial to the defence of the North Atlantic, threatened to leave Nato if the UK did not respect its waters. The Cod War nearly changed the Cold War.

Ruth Davidson, leader of a Conservative unionism that is newly victorious in North-East fishing constituencies, has called for a 200-mile limit like Iceland. This has strong backing from skippers and crews who have just abandoned the SNP and its independence project, partly, some pundits believe, over Brexit. How will it go down in Spain or other nations currently fishing our waters? Well, how did Britain feel when its boats were barred from Iceland’s seas? There will be a diplomatic price to pay for Brexit fishing, whoever is in charge of fisheries, London or Edinburgh. But who will pay it? It might just be the SNP.

However, it is not clear how much, if any, autonomy Nationalist ministers in Edinburgh will get over fishing. But they could end up administering and negotiating that 200-mile limit and sensitive issues like quotas for foreign ships. All that with a local civil service and political class with little international experience and few language and cross-cultural skills. Scotland could be facing a quick diplomatic learning curve.

Nationalists might want to worry about that. A second independence referendum may have been kicked in to the long grass. But the SNP wants a sovereign Scotland, if it ever materialises, to slip seamlessly back in to international institutions, such as Nato and the EU. The mood music towards Scottish nationalism on the continent is less hostile than three years ago. However, any serious divergence from the Common Fisheries Policy or CFP would slow down EU re-entry for Scotland, according to Brussels watchers. Hence the SNP’s two faces on fishing; its local candidates in the North East talked down CFP while the party talked up EU membership. Back in that yellow office in Moscow, the Faroes have Bjørn Kunoy, a French-educated lawyer turned diplomat. He is a published scholar. His specialist topic: the laws of 200-mile limits.