One recent evening I chaired a discussion on our disunited kingdom at the London Welsh Centre. It was a good panel: Professor Richard Wyn Jones of Cardiff University; Tom Holland, the historian and romantic unionist; Adam Tomkins, a professor of law at Glasgow University and adviser to the Scottish Tories; Billy Bragg, the singer-songwriter; and Joanna Cherry, the SNP’s prospective parliamentary candidate in Edinburgh South-West, which is held at present by Alistair Darling. Our discussion was given a charge of energy by the release that evening of Michael Ashcroft’s latest poll of Scottish marginals, which suggested that the SNP was poised to win a majority of Scottish seats at Westminster.

There followed over the next few days a series of panicked interventions from Tory grandees, urging Ed Miliband to rule out any post-election pacts with the SNP. This culminated in the poetry-loving Kenneth Baker, an education secretary under Margaret Thatcher, calling for a grand coalition between Labour and the Tories to save the Union. So far, Miliband has refused to be drawn. Why should he be, when a deal with the SNP might offer his best opportunity of becoming prime minister, something he believes is his manifest destiny?

What was fascinating to me about our discussion that evening was how much consensus there was. No one supported the status quo. Everyone agreed that more devolution, even full federalism, was necessary if the UK was to survive. Each of us conceded that there was no demand in England for regional assemblies or an English parliament, not least because Englishness has for so long – too long – been coterminous with Britishness.

The Cambridge historian David Reynolds, author most recently of The Long Shadow, has correctly called the UK a mini-English empire. Yet it is one that is unravelling, undermined by its asymmetries and internal divisions between a wealthy, entrepreneurial south and a more collectivist north.

This much we know: the centre cannot hold, the British state is fractured, the UK remains imperilled, and we are entering a new era of multiparty politics and hung parliaments. Our first-past-the-post voting system, which was supposed to deliver strong and decisive government, seems no longer fit for purpose when Ukip could win 15 per cent of the vote in May but only a handful of seats. Indeed, a sixth of Scots still vote Conservative but the party has only one MP out of the 59 in Scotland; under a proportional system this would translate into as many as ten Scottish seats, an outcome that would weaken the SNP’s claim that David Cameron has no legitimacy north of the border.

Under the leadership of Nicola Sturgeon, the SNP has repositioned itself as Scotland’s authentic left-wing party. Joanna Cherry, who used to be a Labour Party member, said: “Labour put down its left-wing clothes and we were happy to pick them up.”

Yet in recent days London commentators have absurdly dismissed the SNP as nothing but a “receptacle for protest”. Max Hastings, writing in the Daily Mail, denounced Sturgeon, who is a mainstream European social democrat, as “almost Stalinist”, because she supports redistributive taxation and some kind of moderate land reform, long overdue in Scotland as it is in the rest of the UK, where 158,000 families, the so-called cousinhood, own most of our 60 million acres.

In Jim Murphy Scottish Labour finally has a competent leader. He is a good communicator and campaigner, as he showed on his “100 Streets in 100 Days” referendum tour, during which, standing on a soapbox, he addressed crowds and took a fair bit of abuse in return. But Labour’s decline is deep. Murphy has had too little time to win back some of those voters who feel betrayed by a party that was abandoned first by the intelligentsia (writers, artists, academics and commentators) and then by the poorest and most disaffected.

In the late 19th century, after Gladstone converted to home rule for Ireland, the British establishment, harried by a bloc of nearly 100 Irish MPs at Westminster, failed to answer the Irish question. In time, Ireland was lost and civil and guerrilla wars followed because of intransigence and a kind of magisterial imperial disdain.

In May there could be a formidable bloc of SNP MPs at Westminster, somewhere between 25 and 40 of them, the greatest nationalist force at Westminster since the Irish Parliamentary Party entered into coalition with Asquith’s Liberals in 1910. Their presence will ensure that the main Westminster parties honour their pre-referendum “vow” to the Scottish people (which was written by Gordon Brown, it is said) to create one of the world’s most powerful substate legislatures. Yet much more is needed. There has to be a serious regeneration of local government in England, more decentralisation of power and spending of the kind that George Osborne has begun in Manchester, as well as electoral reform.

The Tories claim to have a long-term economic plan. What is required is a long-term constitutional plan, says Adam Tomkins, one that addresses the grievances of all four nations, such as they are. Scots are not suffering from buyer’s remorse. A majority still wish to remain part of the UK, and there will be a second independence referendum in the short term only if Britain votes to leave the EU, which is unlikely.

In The Crisis of the Constitution, an inval­uable new pamphlet published by the Constitution Society, Vernon Bogdanor quotes Disraeli’s dictum that “England is governed not by logic but by parliament”. But parliament, for all its illogicalities, codes and cherished customs, has to give up more powers – or the Union will be no more.