If Scotland votes to break the union, the future of the west will be imperilled. Perhaps Lord Robertson would dispute such an apocalyptic spin on his Brookings Institution speech on Monday, but there is little hyperbolic exaggeration on my part.

Sounding rather like Gandalf with a sore head, solemnly antigazing at Sauron's armies of orcs massing in Mordor's mountains, the former Nato secretary general claims "the forces of darkness" around the world would celebrate Scottish independence. It would be "cataclysmic in geopolitical terms", he ranted to his American audience; "the dictators, the persecutors, the oppressors, the annexers, the aggressors and the adventurers around the planet" would be handed the greatest gift imaginable. So, a mixed bag then, George.

Robertson clearly has an imagination that should be lauded for its creativity, but it is difficult to imagine a new generation of Visigoths and Mongols preparing an assault on the west if Scotland opts out of the UK. His intervention, however, is just the latest missive in an anti-democratic campaign about which there has been too much silence south of the border.

This former Labour cabinet minister has asked Britain's allies to speak out against Scottish independence – in other words, for foreign countries to intervene in the internal affairs of a sovereign state. Which allies, he does not say: perhaps a Nato member state such as Turkey, whose destruction in the 1990s of 3,000 villages in its war against the Kurds certainly demonstrated a resolute opposition to self-determination.

A few months ago, elite opinion in London took little notice of the Scottish independence referendum, believing that the only matter of debate was how great the no vote would be. But now it is clear the yes vote has The Big Mo: an anti-independence lead that was at 24 points last year is fast dissolving, and a succession of polls have the anti-unionist cause on more than 40%. Bookies report surging bets on independence. The response has been nothing short of an attempt by a rattled establishment to bully, harangue and intimidate Scotland into staying put.

If big businesses and City firms were co-ordinating attacks on policy proposals such as a more progressive tax system or improved workers' rights, the English left would be raging. But too many English progressives treat Scotland as voting fodder, or insurance against an eternity of Tory governments, saving the English from their own poor voting choices.

This is based on a myth – there would have been little impact on the outcome of almost any postwar British elections if Scotland's votes were not included – but this silence still reeks of hypocrisy. It is the English left's responsibility – and nobody else's – to stop England degenerating into a spiteful Ukipland frothing with bile against immigrants and the poor.

However, the relentlessly negative Better Together (or "Bitter Together", as its detractors call it) camp claims it is the other side who are the real bullies. Its chair, Alistair Darling, has spoken of how supporters of the no campaign are monstered by nationalists. He has a point: try criticising the Scottish National party on Twitter, and within minutes a deluge of "cybernats" will soak your timeline in venom. Because I support a loose federal Britain and have criticised the first minister, Alex Salmond, for refusing to back the 50p tax rate and for committing to slash corporation tax, I have endured the novel experience of being labelled a "Red Tory". The Sunday Herald's Iain Macwhirter even dismissed me as "the BBC Question Time's favourite tame lefty" (ouch).

But this is nothing compared with the establishment campaign. George Osborne's warning that an independent Scotland would be kicked out of the pound was swiftly backed by Labour and the Liberal Democrats. The polls showed that the Scottish people called his bluff – and an anonymous minister told the Guardian that "of course" the pound would be shared – but the net effect was to paint a picture of an out-of-touch Westminster elite closing ranks. A senior coalition source has even privately told one Scottish newspaper that a yes vote might not secure independence, which would be nothing short of a coup d'etat against the electorate.

Banks that have offered no public statement of regret for helping to plunge Britain into economic disaster are threatening to up sticks, including Lloyds and the Royal Bank of Scotland. The Weir Group – a company fined for kickbacks to Saddam Hussein's regime – warns that independence would mean higher costs for business. Shell – a company complicit in Nigerian human rights violations – has joined the chorus, along with BP. Fulcrum Asset Management, one of those much-loved hedge funds, claim independence "would be an unmitigated disaster for Scotland". Clearly wishing to woo Scots with charm, HSBC's Stephen King says it will be "a disaster for Scotland, a shrug of the shoulders for everybody else". Charming stuff.

As well as losing the pound, Scots are told they will be stripped of everything from the BBC to EU membership. It's like a loveless relationship in which a partner is told that, if they walk out, they will have their clothes and DVDs taken away, lose all their friends, and be kicked out on the streets.

This establishment campaign is self-defeating, and has left many Scots feeling as though the choice is between hope and fear. "The main achievement is that it has given ordinary people belief they can control their own destiny again," pro-independence author Irvine Welsh suggests, "and they won't be letting go of that notion in a hurry." But whether the bluster and blackmail succeeds or not, it is wrong. It is up to the Scottish people to choose their fate freely, and any attempt push them around is an attack on the very principle of democracy.