A persistent problem for the No campaign in the referendum debate has been the perception it is overly negative and that it is about doing down Scotland.

The added sight of Tory ministers listing the reasons the country cannot become independent also carries the risk of backfiring. There is nothing quite so certain to get many Scots' hackles up as a Tory telling them no.

The intervention of Standard Life in the debate is a different matter and, as a business with almost 200 years of history in Scotland, its anxieties about independence deserve serious consideration. The pensions and savings firm has said it is worried about a number of issues, among them the question of which currency would be used. It also has questions about regulation, taxation and the still-unanswered question about if, how and when Scotland would join the EU. In the light of this, Standard Life says it is preparing a contingency plan to move its operations out of Scotland.

The No campaign seem to believe this is a Dambuster moment in the debate, that a bouncing bomb has been sent towards the SNP. The Nationalists, on the other hand, have dismissed it as more of what they call the bluff, bluster and bullying of the No campaign, with Alex Salmond insisting Standard Life would find an independent Scotland a good place in which to do business, despite the firm's very public worries.

It is certainly true that during the devolution debate in the 1990s there were companies that said something similar to Standard Life and warned a Yes vote would be bad for business; warnings that turned out to be baseless. However, Standard Life was not among them and specifically stated devolution would not affect its business, which makes it all the more significant that it is voicing concerns about independence.

Partly, the concern can be explained by the fact businesses instinctively do not like uncertainty and uncertainty is an unavoidable part of major consitutional change. But, equally, there could be genuine risks for Standard Life in the structures of regulation and insurance if there is a Yes vote. Most of Standard Life's customers are in England, for example, and those English savers could worry about their savings post-indpendence. This is a worry that could make a move to England by Standard Life more likely.

The SNP's case is that these matters could be negotiated after a Yes vote and most companies would almost certainly adapt. But Standard Life's position is nonetheless a challenge for the SNP and its plans for a currency union. The party suggested yesterday Standard Life would have no need to move to England if the UK Government agreed to a currency union, but another interpretation might be that the UK's rejection of currency union would be reinforced by the prospect of Standard Life moving to England and taking thousands of jobs with it.

As Standard Life itself has acknowledged, uncertainty is likely to remain this side of the vote, which makes its contingency plans to move out of Scotland perfectly rational. But what it also does is apply more pressure on Mr Salmond and, as more businesses join the argument on the No side (as they seem likely to), it will be harder for him to dismiss their arguments as bluster, bullying or conspiracy. Standard Life may be the first major Scottish company to warn about the dangers of independence for business, but it is unlikely to be the last.