LET’S start with geography. Scotland lies between the North Sea and the North Atlantic Ocean. Our west coast faces the westering sun and the Atlantic squalls all the way to Nova Scotia. Our east coast faces the North Sea, Scandinavia, the Low Countries, the Baltic and the perishing cold north-easterlies. Due north is the Iceland-Norway Gap.

Scotland is a “big sea” country. It is an island base, perfectly positioned in the middle of these great seas. The seas, and what lies beneath them, have long been a direct source of wealth, from herring and haddock to oil and gas. However, the main value of the sea was always in trade – in buying and selling, importing and exporting. Seafaring is vital to a commercial society and to the profits on which the economic well-being of the nation depend.

Before the Union, Scotland was not an ­imperial sea power. It was, however, a growing “sea state”, whose maritime space was essential to its life and economic interests. It was actively engaged in the sea-space defined by the Irish Sea, the North Atlantic, the North Sea and the Baltic.

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This is Scotland’s corner of the world, ­stretching from Halifax in Canada to Helsinki in Finland. This is the arc of prosperity – and the arc of democracy – and we are right to want a place in it again.

One of the effects of the Union was to turn Scotland’s attention away from this space. The maritime tradition of shipbuilding, ­navigation and trade was maintained, but it was put to ­wider imperial uses. Traditional trading links with the Nordics, Low Countries and the ­Baltic were neglected to pursue opportunities in ­Africa, Asia and elsewhere. The steam ships that plied the trade between Rangoon and ­Mandalay were Scottish built and Scottish owned – and some Scots did well thereby – but Scotland ­itself, Scotland’s trade, Scotland’s ­access to the materials and the markets of our natural ­northern ocean space, diminished.

Today, Scotland cannot trade directly with Ireland, France, Belgium, the Netherlands, ­Norway, Sweden, Finland, Denmark, Latvia, Lithuania, Estonia, Germany or Poland – ­despite these countries being, in maritime terms, right on our doorstep. Most Scottish exports are driven to Dover, where they count for fiscal and statistical purposes as English exports.

That would be bad enough, but the UK has imposed what amounts to a trade embargo upon itself, erecting customs ­barriers and ending the free movement on which ­frictionless trade with our European partners depends. That is intolerable.

Unionists will say that Scotland cannot ­survive on its own. That is true. That is ­precisely why we need independence – to end ­Scotland’s isolation, so that we can regain access to the whole European economic space upon which our future prosperity depends. We want ­independence so that we are no longer so alone.

This has political and strategic as well as economic implications. Last week ­Finland and Sweden formally applied to join Nato. ­Although both countries have a long ­honourable ­tradition of armed neutrality, the move ­received ­overwhelming backing by their ­respective ­Parliaments. In an existential ­conflict of ­fundamental values such as that now ­being played out in Ukraine, the free nations of ­Europe must stand together. There is not much space for neutrality.

What a show of solidarity it has been. ­Norway has offered additional interim security ­guarantees to Finland and Sweden even while the Nato membership application is being ­processed. All European Union countries have similar guarantees to the two aspirant Nato members under the Mutual Assistance clause of the Treaty on European Union.

The Union of 1707 was a bargain struck by Scottish elites who saw hitching themselves to the rising star of English imperial power as a way to gain two things: access to bigger ­markets and security from attack. Both are broken promises.

The UK is no longer the ­highway to the world it once was. It is now a new iron curtain – a “Dover Wall” between Scotland and its European trading partners, waiting to be pulled down.

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Neither is the UK indispensable to our security. British military power (with Jocks in front line, of course) is well and good, but with the end of Britain’s great ­power status, it is valuable only in the context of Nato membership. An independent Scotland could cut out the middleman.

We should stop looking only to the south, over the narrow border, for safety and ­prosperity. Let us turn outwards and look across the wide-open sea. Like the other free, democratic, independent, maritime nations of Northern Europe, it is time for Scotland to “go down to the sea in ships and do business in great waters”.

If we could restore direct passenger and freight ferry services to Zeebrugge or Rotterdam, and finally build that container port in Rosyth, it might be a good start.

Anthony Barnett of OpenDemocracy is this week’s guest on the TNT show. Join us at 7pm on Wednesday