The two sides of the referendum debate do not agree on much, but it seems that an unlikely consensus of sorts has been reached on one issue at least:

Trident. The SNP says an independent Scotland would be free of nuclear weapons and that its position on the issue is not open to negotiation.

Now the Scotland Office Minister David Mundell appears to be saying the same thing for the No side. On Trident, he tells The Herald today, there is no deal to be done. "Yes" in September will mean "no" to nuclear weapons.

Like so much else that is said on both sides of the campaign, Mr Mundell's comments should be approached with caution. Who knows how negotiating positions would change in the event of a Yes vote? But, taken on face value, is what the minister has said good or bad for the Yes campaign?

Seen from one angle, the comments are probably a boost for the SNP. The Nationalists have said for a long time that an independent Scotland would be free of nuclear weapons (despite deciding last year that an independent Scotland would be a member of Nato, the biggest nuclear club in the world). And now here we have a minister in the Better Together campaign agreeing with the Nationalists.

The two sides also appear to agree that the SNP's anti-nuclear position would not be open to any negotiation. Last month Mr Salmond ruled out in the clearest terms any idea of a deal, saying that his opposition to nuclear weapons was not a campaign tactic or a negotiating position. "It is one of the reasons for Scotland being independent," he said.

In agreeing with Mr Salmond that no deal will be possible, Mr Mundell could have helped boost what the SNP believe is a popular plank of their campaign: vote Yes, they have been telling voters, and you will be rid of nuclear weapons.

Not only do the SNP believe this is a seam they can usefully mine in September; polls also show that the overwhelming majority of Scots are opposed to replacing Trident. If doubt remained in voters' minds about whether Trident really would leave Scotland, Mr Mundell's comments may just have helped remove that doubt.

But if the UK Government really has confirmed Trident is off the negotiating table, could there be a down side for the SNP as well? Last month, an anonymous UK Government minister broke from the Better Together consensus and said a currency union would be possible on the basis that the financial union could be traded for Trident. The minister said the UK wants to keep Trident weapons at Faslane and the Scottish Government wants a currency union and that could form the basis of a deal. But if both sides have ruled out such a deal, the SNP may have lost what could have been its strongest bargaining tool.

Of course, it may be that realpolitik will triumph in the end, as it usually does. In the event of a Yes vote, the SNP would want the UK Government to support them on a number of issues, not least currency union and membership of the EU.

On the other side of the table, the UK Government would want Trident to stay on the Clyde because its geographical position and deep waters make it the perfect location. Also, there is no obvious alternative site in the rest of the UK and the cost of moving would be horrendous.

Whether the SNP, having so vehemently committed itself to a Scotland free of nuclear weapons, could in reality negotiate on keeping Trident is another matter. They have consistently said Scotland would be nuclear-free and the government of an independent country would absolutely have the right to demand that nuclear weapons be removed.

However, disentangling the government of Scotland from the rest of the UK would be a complicated, expensive business and require huge compromises on both sides.

The SNP, and now Mr Mundell too, say the presence of Trident in Scotland would not be one of those compromises but the anonymous government minister who spoke out about currency union says it would be. They cannot all be right, which means that, for voters, the uncertainty persists.