SCOTTISH National Party leaders Alex Salmond and Nicola Sturgeon are right to identify the concerted stance by the Tory, Liberal Democrat and Labour parties over sterling “as the Westminster Establishment ganging up” to bully voters in the independence referendum.

They may also be right in concluding that George Osborne’s speech, backed up by Ed Balls and Danny Alexander, was delivered in response to a perceived opinion poll lift for the Yes campaign.

But none of this removes the contradiction at the heart of the SNP call for a formal currency union with the state from which it wishes to secede.

It’s a logical stance since the SNP has made clear that its idea of independence is essentially Indy-lite, with a non-UK Scotland retaining the monarchy and membership of both Nato and the European Union.

Why would an “independent” Scotland want to be part of a currency union with a neighbouring, bigger, more powerful state whose central bank and Treasury would control its taxation, borrowing and spending decisions?

If it wanted a currency over which it exercised no democratic sovereignty, why did Salmond and Sturgeon not plump for the euro?

Salmond himself was not always an adherent of a currency union with what would remain of the UK, describing the pound as “a millstone round Scotland’s neck.”

However, he and his party know that nailing their colours to the eurozone mast would be a kiss of death for their programme, since Scottish voters are as hostile to the single currency as their counterparts in England, Wales and Northern Ireland.

They have seen the ruthlessness of the European Commission and the European Central Bank in imposing deflationary packages on smaller EU states — not least on Ireland which Salmond once lauded as part of an “arc of prosperity” with Iceland and Norway.

His reluctance to share this fate, especially in the wake of the 2008 banking crisis, immediately before which he was writing supportive billets-doux to Royal Bank of Scotland boss Fred “The Shred” Goodwin, has steered the SNP towards currency union with the UK rump.

But how is this a real alternative? It would not give a Scottish government a free economic hand unless that freedom was approved by Whitehall.

Pro-independence critics of the SNP leader’s Indy-lite approach, within his own party, the Scottish Greens, Scottish Socialist Party and other left-wing groups, demand what former SNP deputy leader Jim Sillars calls a “Plan B.”

This would be a Scottish currency pegged to the value of sterling, similar to the relationship that the Irish punt had to Britain’s currency before Dublin opted to trade its independence for subservience to the eurozone.

Could Salmond swallow his pride by suddenly abandoning his currency union position and acceding to that of his critics?

His policies are largely dictated by the poverty of his aspirations and his desire not to frighten the horses by espousing a Scottish republican, anti-capitalist and anti-imperialist stance.

In this he probably reads the mood of Scotland’s electorate better than his left-nationalist detractors who, despite optimistic claims, remain largely marginalised since the SSP implosion and wipeout of its electoral base.

Salmond’s caution indicates, against his instincts, that there is less popular backing for secession than opinion polls indicate and that Scottish workers have more to gain through united action with their English and Welsh comrades than the will o’ the wisp of independence.