Treasury holds Scots to ransom over the pound

The Scottish National Party now has its back to the wall on the pound (Getty Images)

Politicians who oppose Scottish independence call it their “silver bullet”. They have been itching to fire it for months, and finally did so yesterday.

George Osborne, the Chancellor, made common cause with his Labour enemy Ed Balls to declare that an independent Scotland could not keep the pound. Danny Alexander, the Liberal Democrat number two at the Treasury, joined in. So, significantly, did Sir Nicholas Macpherson, the Treasury's most senior civil servant. The cross-party deal is believed to have been brokered by Alistair Darling, the former Chancellor who leads the No campaign.

This is a pivotal moment in the campaign ahead of September's referendum. The co-ordinated strike has calmed jitters in the UK Government over the No camp's narrowing lead in the opinion polls.

The Scottish National Party now has its back to the wall on the pound. But it will dismiss the Westminster and Whitehall stitch-up as a bluff, insisting that the UK Government would negotiate a currency union if the crunch came.

There is a danger that supporters of the Union overplaying their hand. Threats to block full independence if Alex Salmond made “impossible demands” after a Yes vote could backfire.

Of course, it could take years of negotiations to reach “independence day” rather than the 18 months suggested by the Nats. Pro-Union politicians would be advised to stick to the facts rather than suggest they could defy the will of the Scots. Rule one of politics: the people are never wrong.