In Inverness this weekend, the SNP will hold its first conference since winning an unprecedented overall majority at the Scottish elections last May. No doubt the party faithful will be in buoyant mood. Recent polls have suggested growing support not just for Alex Salmond and his nationalist administration, but also for its raison d'etre of independence. Better still, Scotland's two main opposition parties -- Labour and the Conservatives -- remain leaderless and apparently incapable of developing an effective strategy to save the union.

Without question, a key factor in the SNP's current success has been its ability to maintain, as shadow foreign secretary Douglas Alexander put it in a speech last week, a "Mandelsonian discipline". This was necessary during its first term in office when -- as a minority government -- a single dissenting vote could block the passage of any piece of legislation. Yet even in the six months since it took full control of the chamber at Holyrood, its ranks have remained essentially unbroken. The prospect of an independence referendum sometime in the next three to four years seems to have further strengthened nationalist unity.

But outside the MSP and MP groups, there are signs of emerging discontent. In particular, many ordinary members and grassroots activists are disturbed at what they perceive as a shift away from the party's traditional opposition to the stationing of the British nuclear weapons system on the Clyde.

In its submission to the UK Basing Review in June, the Scottish government officially welcomed the decision of the Ministry of Defence to roughly double the size of its nuclear powered submarine fleet at Faslane from five to around twelve or fourteen by 2017. Although not stated in the text, the probable grounds for this are that it would secure the several thousand jobs at the base well beyond the timing of the independence referendum.

The announcement, which ministers were careful not to publicise, followed the publication of an article by Jim Sillars -- whose contribution is significant because of his former status as leader of the party's fundamentalist wing -- in which he argued that Scotland should maintain a form of "military Unionism" with England after independence, including a deal to lease out the Trident base for an unspecified period of time. In the rollicking style typical of the ex-Labour MP, Sillars wrote: "Leasing the Trident base? Jings, crivvens, help ma Boab. Never! is likely to be the first reaction of party members. [But] we must look through the English end of the telescope. Scottish independence, in the old model and old policies, threatens English state interests". There was no public riposte from the nationalist leadership, which tends to be highly sensitive to such radical departures from its script.

The concept of military unionism articulated by Sillars is consistent with the notion of "independence-lite" or "devolution-max" which the First Minister has hinted will be included as a third option on the referendum ballot paper. If this turns out to be the preferred choice of the Scottish people -- and most polls suggest it will be -- it would see Scotland gain full economic autonomy while Westminster retains control over defence and foreign affairs. As such, the possibility of Scotland achieving a quasi-independent status yet still carrying the burden of risk inherent in hosting the UK's nuclear capacity is very real.

The SNP's policy of unilateral nuclear disarmament is a core element in its claim to radicalism -- the nationalist equivalent of Labour's Clause IV. If Salmond was to retreat from it in any way, his party could experience the same moral collapse suffered by Labour under the stewardship of Tony Blair but without the associated electoral success. (A number of surveys show that a majority of Scots are against the renewal of the Trident system.)

So why would the First Minister, famed for his tactical intelligence, take such a potentially damaging step? Well, like Sillars, he may reason that watering down his opposition to the independent deterrent could work to soften London's resistance to full Scottish self-government by reducing the threat it poses to the UK's international standing.

But Sillars and Salmond forget that it is not politicians in London the SNP needs to have on side in order to win the forthcoming referendum; it is people in Scotland, including ordinary party members.

Although the Scottish government has, since June, repeated its intention to get rid of the Trident nuclear submarines, its submission to the Basing Review has created a degree of ambiguity with regard to its longer-standing commitment to make Scotland totally nuclear free. A motion has been tabled at conference which invites the SNP's policy elite -- principally Salmond and his referendum campaign director and Westminster leader Angus Robertson MP -- to reaffirm that commitment. If they refuse to endorse the resolution -- or worse, simply ignore it -- that much-vaunted "Mandelsonian discipline" could begin to unravel just when it is going to be needed most.