Scotland votes next Thursday on whether to dissolve the union with the rest of the United Kingdom, which has survived for over 300 years.

A rejection of independence had been expected, perhaps complacently, until the poll in The Sunday Times last weekend showed, for the first time, a narrow lead for the pro-independence yes camp.

If Scotland votes to leave the UK, there will be serious consequences, and possibly a chaotic couple of years while the divorce is negotiated (including the mandatory bonanza for lawyers). There could also be some difficult consequences for Ireland, north and south.

An explosion in the number of independent states has been a striking feature of world politics in recent decades and the Scots are not the only ones exploring the go-it-alone option. Kosovo, formerly part of Yugoslavia, is well on the way to statehood, Catalonia is planning a referendum on separation from Spain in defiance of the Madrid government and there are separatist movements in many other countries, most explosively in eastern Ukraine, where pro-Russian separatists have initiated a civil war and invited outside military intervention.

Scottish nationalists often query their Irish acquaintances about the nuts and bolts of splitting from the dreaded Sassenachs and establishing the structures for an independent state.

Since Ireland (or a large part of it) did the same thing in 1921, the Irish are presumed to be knowledgeable about such matters. My routine answer, not always welcomed, is that the first century is the hardest. Setting up a new state and trying to ensure its subsequent success is not a task to be underestimated and there have been numerous disappointments around the world in recent decades.

The proponents of Scottish independence base their case on the notion that Scotland could do better on its own, and perhaps it could. But there is an extraordinary vagueness about some of the basics.

The nationalists want to retain the pound sterling, having understandably abandoned their earlier preference for the ill-fated European single currency. But the Bank of England has made it clear that no automatic admission to some a-la-carte sterling zone is on offer. The Scots cannot have sterling and also have monetary independence.

The nationalists want the new Scotland to be a member of the European Union, except that this is not automatic either: they would have to negotiate entry and all current member states would have a veto.

States which are resisting secessionist movements, such as Spain, are quite likely to resist Scotland’s application to join the EU. They will fear that a Scottish secession followed by easy entry to the EU would inspire separatists in Catalonia, in the Basque country and even in the Canary Islands.

There are regions of Italy which have secessionist tendencies, including Lombardy, the Veneto (northeast) and Sardinia. Separatists in Corsica seek independence from France, resisted by Paris.

The United Kingdom seems to be about the only European country willing to permit its regions to vote themselves out of the state.

Two issues alone, the currency and EU membership, could create political deadlock if there is a yes vote on Thursday.

But there are others: Scotland’s divorce terms with London would have to include the acceptance of responsibility for a portion of the UK’s national debt and there is no guarantee of agreement.

The UK is a member of NATO. While Scotland would also join NATO according to the nationalists, it would be nuclear-free. So all of Britain’s seaborne nuclear capability would have to re-locate to the rump UK, since it is all currently based in Scotland.

Why would NATO admit Scotland in these circumstances? Would the nuclear submarine bases end up on Lough Foyle? Would a free Scotland, excluded from NATO, have to shoulder big costs for defence?

Ireland and the UK have long operated a common labour market, passport-free travel and relaxed rules about dual citizenship. These would cease to apply to Scotland once the new state was established and there would be an international frontier, not just between England and Scotland, but also between Northern Ireland and the new state.

Thursday’s vote is being held in advance of any clarity about these and a host of other important practical issues.

The most immediate impact of a yes vote would likely be in the financial markets. Both of the big Scottish banks went under during the UK banking crisis. They were rescued by the treasury and the Bank of England.

Fears that an independent Scotland could not support these mammoths (they are huge relative to the size of Scotland’s economy) could force them to re-locate outside Scotland, with attendant job losses.

There could even be a drain of deposits from these banks in the short term, since people would see them as exposed to new political risks.