THE gloves are off.

After David Cameron blew kisses at Scotland last week, this week it was the turn of George Osborne's currency union haymaker punch, helped on by his supportive seconds of Ed Balls and Danny Alexander.

Of course, Alex Salmond often seems to thrive on confrontation and he responded in characteristically robust fashion, denouncing the attack for its three bs - bullying, bluster and bluff. He could have added a fourth - brinkmanship.

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It is worth noting the irony in all of this that, in terms of the currency, the First Minister and his colleagues are the unionists and the Prime Minister and his colleagues are the separatists.

Mr Salmond's staunch defence of his preferred option of a currency union might be manageable for the moment but as the September poll nears and No, No, No continues to be the unified Whitehall refrain, it could become unmanageable. The pro-UK forces now think they have him on the run and at some point the mighty Eck will crack.

Indeed, observers have already detected how Mr Salmond has been emphasising the "range of options" open to the Scottish Government and mulled over by the Fiscal Commission, which plumped for currency union with the UK.

Are the likes of the Chancellor, his Labour Shadow and the Chief Secretary to the Treasury really bluffing? Only time will tell but one well-informed Whitehall source suggested: "If it is, it's some bluff."

One view is the Whitehall hardball will cause offence in Scotland and simply entrench the Yes vote. This might well be the case among diehard independence supporters but could the unified and consistent rejection of a currency union sow more doubt in the minds of the undecideds? This is what the Coalition is banking on.

One of the Prime Minister's senior colleagues suggested to The Herald Mr Salmond's declared Independence Day of March 2016, ie a negotiation period of 18 months, was simply unachievable given the complex issues Holyrood would have to discuss with Westminster.

The source then followed through the train of thought of a no-deal by March 2016 and suggested independence would not happen, could not happen, because there was no agreement on the table. In this scenario, the default option would be that the UK would continue as is. Indeed, some parliamentarians have suggested intergovernmental talks between London and Edinburgh could take the best part of five years to complete successfully. What happens in the meantime?

To add to the sense of the UK Government playing hardball, the senior Coalition source made clear that post any Yes vote, the Coalition's priorities would be to look after the interests of the people of England, Wales and Northern Ireland and there was no way it would bow to impossible demands from Mr Salmond's side.

Mr Alexander yesterday popped up to insist the referendum result would be "respected, full stop, end of story" but failed to say what would happen if there were no agreement by Independence Day.

Recently, academics were asked this very question. There was a stony silence and then one replied: "Chaos."