If the United Kingdom collapses, it will not be because a majority of Scots are hell-bent on leaving but because the UK government is giving up on saving it. No union can survive without unionists and, after an election in which, to head off Ukip, the Conservative and Unionist party presented itself as the English Nationalist party, it is clear that the union is on life support.

Some unionist commentators are comparing the post-referendum Scotland of 2015 to the post-referendum Québec of 1995, comforting themselves that support for Québec’s independence has fallen from 49% in 1995 to just 25% now. But there is a big difference: whereas the rest of Canada has consistently stood as one to keep Québec in, it is London’s equivocation over Scotland that is becoming the greater risk to the UK.

For while no one should disguise the enormity of the nationalists’ election victory, it would be wrong to assume that the dramatic results signal any further rise in support for independence since last year’s referendum. Having discovered in their polling that the repeated mention of independence or a second referendum did not assist their vote, the Scottish National party dropped both from their manifesto and have since been relegating fiscal autonomy into some far off future.

Gordon Brown: UK on life support as Conservatives play the English card Read more

While Scots are strongly Scottish, and demonstrated at the election that they want to be represented as Scots, it would be wrong to automatically equate patriotism with nationalism or assume that the popular demand for change is more about a change in borders than about the social and economic change that people urgently want – and have yet to see – in their lives.

However, in the last few weeks SNP and Conservative politicians have descended into a sectarian war of words, raising the spectre of Scottish and English “vetoes” and suggesting there are irreconcilable differences between the two nations.

Now claiming that the UK should not leave Europe unless all four nations vote “no” to Europe, the SNP are championing a dubious constitutional principle even for nationalists: that any one nation of the UK can block the decision of the other three nations. The irony is that in enunciating such a principle that subordinates the interests of the UK as a whole to the sectional interests of one nation, not just Scotland but Wales, England and, even more controversially, Northern Ireland could have a veto that frustrates the rest of the UK’s will.

But instead of the new Conservative government exposing the illogicality of such vetoes and emphasising – as the government of the whole UK – what binds all four nations together, ministers are now promoting the idea of an English veto. It started with English votes for English laws, which would make Scots second-class MPs in the House of Commons, able to vote on only some issues.

It continued in the sectionalism of their “English election manifesto.” It intensified with their poster campaign – the Ed Miliband puppet on strings pulled by Nicola Sturgeon or tucked into the pocket of Alex Salmond – which conjured up the idea of the Scottish menace and was designed to whip up English nationalism against Scottish nationalism. Even more insidious is the little-known Carlisle principle enunciated by David Cameron: that each year the UK government would scrutinise and, in effect, second-guess the work of the Scottish parliament.

By focusing on exposing how much Scotland’s decisions could harm England, they are subordinating the interests of the UK as a whole to the sectional interests of their English vote. In a tit–for-tat retaliation to the SNP playing the Scottish card, the Conservatives are playing the English card.

When Scotland’s future was at stake in the referendum, Scots had to choose between Scottish nationalism and support for the union – and many patriotic Scots like me chose to defend the union. But when it has come to a choice between English nationalism and defending the union, the Conservatives are choosing English nationalism.

Sadly, this tactic – to divide and rule and put party before country rather than to unite – is one that the Conservatives can return to again and again.

It reveals a bigger truth: that while Scotland has not yet written off Britain, the Conservatives are starting to write off Scotland.

And as the nationalists inevitably try to claim a divergence of opinion between Scotland and England on welfare cuts and austerity, over our future in Europe and the replacement of the Human Rights Act, more and more people will be tempted to conclude that the union has become unworkable.

There is a way through. As a start, we should embed a new constitutional principle that recognises the real glue that – far more than flags or anthems – binds the country together: the pooling and sharing of risks and resources to uphold basic social and economic rights – from common pensions and free healthcare to guaranteed help when sick, unemployed or disabled – across the UK’s nations and regions. We should state clearly that whatever else any government at Westminster does, it will uphold – and even the most rightwing government will be unable to abandon – the principle of equity between the nations and regions, allocating resources on the basis of need, and that it will protect established social and economic rights.

A few years ago, I tried but failed to gain popular traction for a clear statement of the values that tie all four nations together– a first step to a written constitution for Britain. Now I would call for a constitutional convention to debate and set out the rights and responsibilities of citizens in each part of the UK.

If the current government will not lead, we should bring together a people’s convention that opposition parties – Labour, Liberal Democrats, Greens, Nationalists and others – and interested civic society and faith groups might join. Such a convention which would examine votes at 16, the replacement of the House of Lords by a Senate of the regions and nations, and what could add up to a quasi-federal territorial constitution would elevate the debate on citizens’ rights above the current narrow and blinkered Conservative focus on removing rights rather than affirming them.

In a Britain where the battered forces of progressive opinion urgently need to regroup and find common purpose, a constitutional guarantee to citizens of all four nations could be the best way, and perhaps the last chance, to show there is a clear and explicit vision of how the four nations can achieve more together through cooperation and sharing than we can ever do by breaking apart.