The debate about Scotland's future is hotting up, and it should not come as a surprise that oil has provoked the conflagration.

The stewardship of North Sea oil has been a touchstone issue for nationalists since the early 1970s when the rallying call "It's Scotland's Oil", gave the SNP its first breakthroughs.

Alex Salmond's remarks about being "among thieves" at Westminster is a clear reference to the sense of grievance felt by many of his grassroots supporters at the alleged squandering of this resource by successive UK governments.

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It will undoubtedly play well with the SNP's footsoldiers, but such language cheapens the debate. Not that the remark is likely to have been ill-considered. On the contrary, with a media spotlight on the north east as both UK and Holyrood cabinets met there, it was surely carefully weighed beforehand.

Baroness Goldie, the former Scottish Conservative leader describes it as yah-boo politics. She is right to say that it adds nothing helpful to the discussion, in terms of content at least.

But neither side is covering itself in glory in terms of constructive debate. Some would argue the Better Together campaign has been equally as negative as Mr Salmond. The Prime Minister's comments yesterday that the oil industry was best borne on the UK's broad shoulders are an example.

Claiming Scotland could not afford the tax breaks currently on offer from the UK to develop new fields and decommission old platforms is simply bizarre. Tax breaks are by their very nature affordable. A government need not take any tax at all.

Opponents of independence - whether it is George Osborne, David Cameron, the UK cabinet or Better Together - can surely do better.

Asking Mr Salmond how he can afford the plans he has set out in the independence white paper Scotland's Future, while maintaining current levels of tax take on the oil industry, is legitimate. Likewise, the Yes campaign could be asked similar questions in the abstract, such as whether predictions about Scotland's future economic wellbeing can be realised without placing a greater tax burden on oil companies.

But suggesting Scotland simply cannot afford to manage the oil industry insults the intelligence of Scottish voters.

It is in this context Mr Salmond's provocative remarks about "thieves" at Westminster should be read.

The Yes campaign believes Better Together is adopting fear tactics and may suspect they are working. It is also riled at Mr Cameron's continuing refusal to debate independence with Scotland's First Minister.

Oil gives us many things, from fertilisers to plastics, energy for our homes, fuel for our vehicles. It generates light and heat.

There has been a strange lack of passion and engagement in the debate so far. Mr Salmond's reference to "thieves" is not in itself constructive. But some heat is welcome, and it drew attention to his key claim - that examples such as Norway show small countries can handle oil and gas resources as well as or better than large ones.

As long as the First Minister's comment generates as much light as it does heat, then it should be forgiven.