The issue would come up whenever party leader Alex Salmond visited the United States, while it provided an easy target for political opponents, who implied that the security of an independent Scotland might be compromised.
Some within the party pushed Salmond to ditch the policy when the SNP became a genuine contender for power post-1999, but at that stage the SNP leader did not want to pick a fight with his party.
Only late last year was there movement, when the First Minister told the US magazine Time that an independent Scotland would consider an “alliance” with Nato.
In recent weeks, senior SNP figures – chiefly the party’s defence spokesman, Angus Robertson – have become noticeably circumspect on the Nato issue, and now it seems likely that a meeting of the national council in June (usefully closed to the media) will “discuss” whether or not an independent Scotland would remain in Nato.
This, of course, is not the first time the party has shifted position on a key policy.
First was the monarchy – when the Nationalists ditched the plan for a post-independence referendum – and, more recently, currency: retaining sterling and, therefore, leaving the Bank of England in control of monetary policy.
Plans for the BBC post-independence have also been toned down.
If the Nationalists’ position on Nato is reversed, it will be unusual in having been put to the party first (although the SNP claims that the party did, indirectly, endorse the new monarchy policy at its 2007 conference).
Although Nato is not a “red line” issue for the SNP, a minority – including some MSPs – still dislikes it.
If discussed at national council, there is sure to be a lively debate.
That said, if the leadership has decided to change the Nato policy, then it would happen.
In the battle to win hearts and minds ahead of the independence referendum autumn 2014, the SNP increasingly ranks external political credibility above the views of its members.
A shift on Nato is all part of the grand plan to persuade apprehensive voters to stop worrying and learn to love independence.
What the US-dominated alliance would make of an independent Scotland wanting to be a member while refusing to countenance nuclear weapons is a moot point, although states can, of course, become “non-nuclear” members.
There is a danger in all of this. The distinction between pragmatism and expediency is a fine one.
Political movements need unique selling points, and if opposition to Nato goes, then the Scottish National Party’s boils down to removing nuclear weapons, gaining oil revenue and some limited fiscal autonomy.
The party has to bear in mind that “vote for independence and almost everything will stay the same” is not much of a rallying cry.
• David Torrance is a political commentator and biographer.