The invasion of Ukraine has generated debate in Ireland about its traditional neutrality. Meanwhile the SNP’s recent setbacks may allow wider debate on an independent Scotland’s defence posture.

Until now the SNP has said that an independent Scotland would be in Nato but not host nuclear weapons. If independence were imminent, this policy would present serious challenges. The US should be an available and important friend to a new Scotland. While American policy-makers would not welcome further weakening of the UK, this might be balanced by a popular sentimental attachment to Scottish independence, in a curious muddle including misty notions of Bonnie Prince Charlie and Irish American enthusiasm for “Celtic” breakaways from the Saxons. But the US would instantly become more hard-nosed if there were any threat to the ability of US nuclear submarines, both nuclear weapons capable and nuclear-powered, to visit Faslane, or to the ability of the continuing UK navy to maintain a nuclear deterrent within Nato. No potential government of an independent Scotland should underestimate how immediately unfriendly the US could become if we messed around with either of these.

The SNP has got into a bind on this, making commitments to itself and to Scottish voters that are hard to get out of. But if independence is now on a longer timetable, a wider debate on the issue may be possible. One option might be contributing to Nato by letting Faslane’s base continue – incidentally preserving its thousands of jobs. There might even be scope for a rental agreement, generating useful cash.

Ireland has long got away with not allowing US nuclear-powered ships to visit. This may in part reflect the strength of the Irish American lobby, which would not approve of the US testing Ireland's resolve on nuclear issues, let alone sharp sanctions like those the US imposed for decades on New Zealand when it barred nuclear powered vessels.

Ireland’s neutrality began with a widely-supported historic wish to keep its military distance from the UK (though there have been important but discreet exceptions to this in practice). On the back of that, a more positive support for the principle of neutrality has developed, even if somewhat undefined. Concern for this led Irish voters to reject the EU’s Treaty of Nice in 2001, until winning EU assurances on defence commitments. Russia’s invasion of Ukraine, the subsequent rapid abandonment of Finland’s and Sweden’s attachment to neutrality and their Nato applications, and the public emergence of some longstanding UK-Irish defence arrangements like the RAF’s role in defending Irish marine airspace, have thrown the debate open. Irish Foreign Minister Micheál Martin has encouraged debate; the normally sure-footed, largely ceremonial President Higgins has come controversially close to a public intervention against change.

Irish Nato membership seems a long way off. But a more dynamic involvement with EU military arrangements seems likely. The US will look benignly on any greater Irish involvement in western defence, however defined. But they would not look kindly on a new Scotland disrupting existing Nato structures, especially nuclear ones. People can reasonably argue that Scotland would have the right to cause this disruption and take a principled anti-nuclear stance. But we would also need a proper examination of the costs, including entering on the international scene with the US as a seriously angry critic.

George Fergusson is a retired senior diplomat