Perhaps we misheard.

Perhaps, during all the months and years of argument and campaigning, no Conservative or Labour politician said time and again that holding the United Kingdom together was a cause surpassing all others. It seems that was a misunderstanding.

But here we are. William Hague has a half-evolved scheme that, if brought to fruition, will be the end of Westminster as it has existed since the Union of Parliaments. Gordon Brown meanwhile turns up with a couple of devolution proposals apparently retrieved from the "offer them anything" file. And these are the people who said they would fight to the last ditch for the UK?

Here's the ditch. It's a busy trench this January. For the most part it seems to this observer to be filled with folk less concerned with the future of the kingdom than with scraping together a Commons majority by any means necessary. Perhaps we could judge them accordingly.

Tory attitudes were plain enough on the morning after the referendum before. No sooner had Scotland missed its chance than David Cameron was out in the road in front of Number 10 proclaiming that "English votes for English laws" was a reform whose time had come. In fact, it was necessary "in tandem", no less, with whatever Scotland had been half-promised. Of dancing in the streets, there was none.

That might be because the Prime Minister left Mr Hague with the task of squaring a circle. English votes are easy to identify. Our friends in the south, of whatever party, have 84 per cent of the voting power in the Commons. If England's national interest is the only issue, there is no problem, for less a West Lothian Question. Those who hanker for an English parliament need not fret. They have their legislature.

"English laws" are another matter. Can anyone name one of those things? Is there a single piece of conceivable legislation guaranteed to have no consequences for those in these islands who happen not to be English? Mr Hague mentions education (a half-truth), health (an untruth), and - astoundingly - taxation. Even the American federal republic would not risk that political nightmare. No federated system would or could.

Mr Hague has attempted to sketch a racehorse and designed a three-legged camel. Like Mr Brown, he invites the stubborn Yes voter to wonder again why it was so important to keep that devo-max thing off the ballot paper last September. Implicit in the Tory scheme is the recognition that Scotland can acquire any powers it fancies as long as Ukip types can be bought off. Explicit in Labour's latest plans is simple bribery.

Neither party now bothers to put principle at stake. Both remain wedded to attitudes familiar from the days of Ted Heath and Jim Callaghan. It amounts to "What must be give the Scots this year?" The new wrinkle is the Conservative understanding, under duress, that English voters have democratic rights too.

No rational person who voted Yes last year ever doubted the fact. Self-determination, if it means anything, has a universal application. But a number of Scots have been kicking up a fuss for a generation for reasons that have less to do with chauvinism than arithmetic. Set 84 per cent against the rest and attempt to invent a workable legislature. Give that percentile the belief that they are subject to a minority veto: how united is your kingdom?

The essential political fact of our 21st century is the acceptance within the UK that if Scots demand the right to follow their choices, no one can or should stop them. In Spain, Madrid forbids even Catalonia's right to vote on independence. Mr Cameron neither desired nor dared to attempt such a strategy. Mr Brown meanwhile speaks for a party that is these days "patriotic". And both men fight, so they say, for the UK.

In reality, they tunnel at the foundations of the edifice. Why? Don't the Tories grasp that an "English veto" extended to taxation - I paraphrase Mr Hague only slightly - is the end to another auld sang? Doesn't Mr Brown, who grappled for so long with the intricacies of benefits, grasp that throwing Holyrood another couple of bones will light fuses in Cardiff, Derry and Liverpool?

You might guess that I'm not too fussed. If the great men of Westminster are purblind, I reckon it a stroke of luck. I am surprised, however. I don't buy the idea, for one thing, that the likes of Mr Hague or Mr Brown fail to care about agitation among the Scots. The huge effort expended on stopping a Yes vote last autumn was evidence enough of a British state with a sense of self-preservation. Yet now, daily, they throw it all away.

For the most part, it's just a resumption of party politics. Mr Hague's party has a Ukip problem below the Border. Mr Brown and his friends are terrified by a massive collapse in trust among Scots. Promiscuity with promises is a General Election tradition. It is a measure of the desperation obvious in both parties, however, that they are ready to make chaff of the constitution just to drag themselves to the end of the first week in May.

Mr Hague has come up with a scheme that will satisfy neither the Little Englanders, nor the politicians in devolved legislatures. The Leader of the House seems not to know - or perhaps care - how taxation works, or what exactly has been offered, in theory, to Holyrood. It doesn't much matter how you dress the thing up: once you define a difference between one member of Parliament and another, there is no United Kingdom.

The Scots have had their vote, it might be said, and will get no other. The reaction of Scottish voters is of marginal interest to those trying for a Tory majority: on their better days, Scottish Conservatives dream of three - they can even count them - MPs. For Mr Cameron, the fact is, and must be, trivial. If Scottish Labour is yet again suffering because, yet again, it picked the wrong leader, there will be no Tory tears.

You watch them at work, nevertheless, and you see the UK crumble before your eyes. You are struck by the fact that this is more obvious to those who voted for Scottish independence than it is to Mr Hague, Mr Cameron, or Mr Brown. An English veto? A Balkanised social security system? You don't see the logic in any of this?

These count as marks of desperation, no doubt. They are shoring up their trenches. People in those old, familiar parties are confused and ready to grasp at every straw. When Lord Ashcroft publishes his Scottish polling numbers today there will be another round of swings and roundabouts. But the essence of the argument will remain.

Either your kingdom is united, or it is not. If the latter, what's the choice? A bribe here, a bargain there, some desperate stratagem striking at the constitutional heart of the thing you were supposed to be defending? Try that. Why not? Listening to Mr Hague and Mr Brown, I make the guess that it's the best the UK has.