It was once said of the Brookings Institution that "if think tanks themselves were countries, Brookings would have aircraft carriers".

Among those who ponder policy for a living, the organisation based on Washington's Massachusetts Avenue is as big and as influential as they come. Nice to see it spares some thoughts for Scotland.

In point of fact, Brookings has called on Lord Robertson of Port Ellen, former stalwart of Nato, new Labour and the GMB union, to fill in any gaps in its knowledge of the north European Atlantic fringes. Specifically, the peer who once said devolution would kill nationalism "stone dead" was asked for thoughts on a referendum hereabouts on September 18. If he was taken seriously, the Pentagon has just gone to defcon one.

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We have established, I think, that some people believe independence for Scotland would be a bad idea. We know there are those who deplore the idea that the United Kingdom could be reduced to a rump. We've all heard of patriots who despise any version of nationalism that isn't the British variety. What we hadn't yet encountered was a case against independence that could make The Day the Earth Stood Still sound pedestrian. Other Unionists make do with routine prophecies of doom. Lord Robertson will settle for nothing less than a "cataclysm", up to (and not necessarily excluding) the fall of the West. On this reading, Yes voters could put the entire world order at risk. Who knew?

Lest you think I'm joking, what Lord George said was this: "The loudest cheers for the break-up of Britain would be from our adversaries and from our enemies. For the second military power in the West to shatter this year would be cataclysmic in geopolitical terms." Someone will no doubt be along shortly to call that a positive case for the Union. For now, it makes you wonder just what was going through Lord Robertson's mind when he was Nato's secretary general or, for that matter, the minister responsible for the UK's nuclear weapons. This is how he saw the world and Britain's place in it?

Apparently so. The peer, who among other things serves the Washington-based Cohen Group in "providing advice to corporate leadership", also said: "If the United Kingdom was to face a split at this of all times and find itself embroiled for several years in a torrid, complex, difficult and debilitating divorce, it would rob the West of a serious partner just when solidity and cool nerves are going to be vital. Nobody should underestimate the effect all of that would have on existing global balances and the forces of darkness would simply love it."

Let's be clear. The Brookings Institution is a very serious outfit, one accustomed to hearing serious ideas proposed by some of the finest minds available. On this occasion, presumably due to a booking mix-up, it heard the suggestion that those who vote for independence will ally themselves with "the forces of darkness". Vladimir Putin? Al Qaeda? The makers of Britain's Got Talent?

Britain's got Lord Robertson. You could almost sympathise. The veteran Atlanticist, who long ago forgot to distinguish between loyalty to the United States and any local ties, wants us to believe, first, that the UK's military power is significant; secondly, that it could be lost entirely if 8.5% of the population exercise a right to self-determination. Then he wants Americans to buy the idea that this deserves to be called a cataclysm.

If he means every word, there is a streak of authentic paranoia running through Lord Robertson's analysis. It falls to him, it seems, to tell Scots and Catalans and Belgians how to run their affairs. If they refuse to obey, only chaos and cataclysm await. The "forces of darkness" line would be a nasty enough jibe were it not so hilarious, but that isn't the end of it.

There is, for example, the ugly suggestion that "the Northern Irish who would see a reappearance of old demons" if Scotland voted for independence. There is the creepy innuendo provided by yoking together the First World War centenary with the possible "fragmentation of Europe" to provide "an irony and a tragedy with incalculable consequences". All this because you feel entitled to a country you can call your own?

One consequence of independence, easily calculable, would be an end to the posturing of Lord Robertson and other pensioners from the military-industrial complex. He turns his rhetorical amplifier up to 11 for a reason. His is language typical of the people who turned the effort to curb terrorism into a perpetual war in which any excuse, even a democratic referendum in a small country, will do. His is also the language of those who fear that losing an argument means losing control.

Lord Robertson, this Scot within the British establishment, still sees his country in terms as old as the Union: we are needed to make up the military numbers. He doesn't waste time with those "positive contributions" or bonds of affection. In essence, he is accusing Scots of letting the side down just by contemplating a reduction in London's power. And by London's power he means the power to assist Washington whenever required.

The peer isn't just inveighing against nationalism. He is speaking out, so he believes, on behalf of the global order he has served through most of his career. His is the dispensation that gave us Iraq and Afghanistan, Guantanamo and GCHQ. Lord Robertson is front and centre among those who maintain Scotland as a repository of WMD. Yet he denounces a few million Yes voters as the tools of "our enemies". So much power in a few ballot papers. Nevertheless, fantastic as the language is, his lordship manages to be both genuinely insulting and threatening. It turns out that those Yes voters handing out leaflets on street corners and arguing in village halls risk "giving the dictators, the persecutors, the oppressors, the annexers, the aggressors and the adventurers across the planet the biggest pre-Christmas present of their lives".

It's less a red scare than a blue and white saltire-effect scare. Against stiff competition, it counts as the most lurid, demented peroration a Unionist has managed thus far. The search for this month's winner in the referendum shocker stakes can be called off. Lord George has won the rosette, the certificate, and the chance to audition for the Dr Strangelove remake.

It's quite a bomb he's dropped. Unfortunately for him, all the casualties will be on his own side. An argument for the Union surely has to stay somewhere within the vicinity of plausibility. The idea that the Western alliance depends on Scotland's contribution to the UK's diminishing contribution is liable to cause hollow laughter in the White House and the Pentagon. It will certainly cause hilarity in every other quarter.

One tip for Lord Robertson and his kind: you'll never be able to deal with the demand for self-determination, chaps, if you don't make even a wee effort to understand it. We understand you only too well, after all. If comedy night at Brookings was a guide, you're just not trying. And that is funny.