It’s not fair, cries every child. “Life’s not fair,” retorts every parent. Both sides then wrestle with the crooked timber of mankind to decide who gets the first piece of cake. The purpose of politics is to help them, to minimise unfairness and to fashion a path to compromise.

September’s Scottish independence referendum is coming to seem anything but definitive. It was not the final answer to a question, rather a stage in a process. That process is clearly one of ever greater separation for the component parts of the United Kingdom, a separation that was obvious from the day in 1921 when Ireland began to dismantle the “first British empire”. It did so not because Irish people really wanted it, but because the London government was so incompetent at regional autonomy.

It still is. This week the leader of the Commons, William Hague, picked over the referendum battlefield. He found many a blood-stained promise, torn concession and mutilated pledge. David Cameron had promised the Scots “a vow” of devolved powers with unlimited subsidy. The Scots accepted the bribe and deserted the field.

The prime minister then made the most inept of interventions. Despite pleadings from fellow unionist campaigners, he promised angry English Tory MPs that he would grant them balancing powers in the matter of English legislation. “Now the millions of voices of England must be heard,” he said. It was unfair that Scottish politicians should control their own services while expecting English taxpayers to finance them, while remaining free to vote on English services. If English MPs were to be “second class” in Scotland, why should Scottish MPs not be as such in England?

Cameron’s argument was fair but its timing was crazy. It seemed to jeer at the yes campaigners when they were still smarting from defeat. Scotland had indeed got away with constitutional murder. Having sought independence and won enhanced autonomy, they still wanted all the goodies of union. They wanted the full Barnett formula subsidy and legislative power to influence England’s domestic administration and budget. But this is what Cameron had promised, with no mention of strings attached to make it palatable to English Tories.

Cameron thus got the worst of all worlds. Neither Labour nor the Liberal Democrats have been ready to sign up to Hague’s “English votes” proposals. As a result, Cameron has had to back down on linking this “in tandem” with the recent Smith commission proposals on fiscal devolution, and may have a Tory revolt on his hands. He has snatched defeat from the jaws of victory.

Relations between Scotland and England will never settle until an agreed constitutional autonomy – “devo max” or “indie-lite” – is formally in place. All big countries are federations of some sort. The sharing of power between the centre and semi-detached provinces is always contentious. Ask the Sicilians, the Catalans, the Montenegrins, the Corsicans, the Québécois. Sometimes argument leads to civil war, sometimes to partition. Sensible countries forestall this by summoning their wise and good to rebuild their constitutions.

The inept way in which London has handled Scottish aspirations in the quarter century since the poll tax is what brought about the present crisis. It repeated London’s response to Irish nationalism in the 19th century. The referendum has now led to an undignified search for some Scottish “tax-raising” powers (the Smith commission), and in return Hague’s impenetrable options for qualified Commons voting. The Tories are desperate to have Scots MPs out of their hair, for fear of Ukip. Labour wants the opposite, for fear of conceding seats to the SNP and losing a possible future Commons majority. The result is stalemate.

The destination of all this is clearer than the means of getting there. Some independence under the crown will one day be granted to Scotland. There are many models for this, but all demand a sincere curb on central power. Texan congressmen do not tell Coloradans how to run their drug laws. Madrid politicians do not fix Basque tax rates. Near-autonomous Greenland has just two members of Denmark’s Folketing, and in 1985 unilaterally withdrew from the EEC. Get these things right and all is well. Get them wrong and you have a Bosnia or a Kosovo.

At the root of such devolution lies fiscal responsibility, the path down which the Scots are now tentatively being led. It is absurd that this should not mean reduced representation in the UK parliament. The Hague plan for 59 Scottish MPs to continue wandering round Westminster is like a parliamentary dock-work labour scheme, MPs paid to do nothing. As a halfway house to autonomy, a shrewd SNP would volunteer to slash by two-thirds Scottish members at Westminster. It would lance the boil of the West Lothian question by making it unlikely that Scots would ever “swing” a vote on English laws.

Meanwhile the rest of the UK stumbles chaotically down much the same road. The Greater Manchester devolution plan is emerging as distinct from the “city deals” negotiated by the business minister, Greg Clark. Wales is in modest turmoil over how many new powers should be granted to Cardiff. Over-governed Northern Ireland is finally seeing its power-sharing executive, sustained by lavish London subsidies, lurch towards collapse.

No other democracy would approach constitutional reform this shambolic way. Enthusiasts should read of the framers of America’s 1787 constitution – for a country with roughly the population of today’s Scotland. The revolutionary articles of confederation led to a “committee of the whole”, then a splendidly named Great Compromise before passing on to a “committee on detail”. In comparison, Tuesday’s debate on devolution was a bar-room brawl. America’s constitution may have needed much reform, but its drafters recognised the nobility of their task. They knew it was a compromise that should embody the character of the nation.

British politicians have come to hate royal commissions. They think they diminish their own discretion and status. They are right, which is why a commission on the constitution is now so urgent. All of Scotland, Wales, Northern Ireland and the regions, cities and counties of England may not be ready for full or even partial autonomy. But their ambition for more self-rule is real. They deserve more consideration than they are getting from today’s dumbed-down London parliament. The way it is going, the union is doomed.