ON paper, it must have looked like a well-calibrated battle plan.

Strike one: Philip Hammond, the Defence Secretary, travels to Glasgow to talk up the Union defence dividend and talk down the notion of a part of the UK breaking away. Strike two: a phalanx of ex-military top brass break cover to warn of the "dark shadow" that would engulf an independent Scotland if it abandoned the ultimate deterrent. Strike three: the First Sea Lord launches a broadside to insist a Yes vote would damage the "very heart" of Britain's maritime defence capability. In practice, though, the barrage misfired.

Firstly, with Whitehall acknowledging the pro-UK offensive was too negative, who should pop up with a tale of cataclysm and the forces of darkness but Lord Robertson, ex-Nato Secretary General and ex-Defence Secretary, who has form on predictions.

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Secondly, David Mundell, the Scotland Office Minister, set the wrong co-ordinates for his contribution when he insisted, actually, the Coalition accepted Alex Salmond's red line on Trident. This looked remarkably like a pre-negotiated white flag.

Thirdly, Mr Hammond insisted nothing was non-negotiable in "any negotiation" — not just one on defence matters — and that everything would be on the table should Scots vote Yes. This understandably prompted people to point out how Westminster had for weeks told us how the SNP's unionist desire on sterling was a non-starter.

In fact, when the Secretary of State told this newspaper everything would be on the table in a post-Yes vote, he was simply, ahem, telling the truth.

The UK Government might have a red line on a currency union and the Scottish Government might have one on Trident but each will make sure both issues are at the centre of what will be a very large negotiating table should a vote for independence come to pass.

Given the anti-independence barrage, the First Minister, understandably, felt the need to strike back and, not only reiterated — to cheers — how an independent Scotland would banish nuclear weapons but also gave a personal guarantee the Royal Navy would continue to build its warships on the Clyde because Scottish shipbuilders were the best in the world; or words to that effect.

What Mr Hammond and his colleagues will have to take away from this week is that they have to take a leaf out of the Nationalist war manual and adopt a far more positive, upbeat approach to ensure that claims of emotional blackmail cannot be made by ordinary voters so easily.

In this referendum of the head and the heart, the best line of defence is not always attack, attack, attack.