David Cameron just can't help it; he can't resist dancing to Alex Salmond's tune. The Tory leader has once again let it be known that he intends to cut Scotland's funding and strip Scottish MPs of their voting rights in Westminster. The weekend press in England was dominated by the threats, a counterpoint to Alex Salmond's celebration in Aviemore of his first conference as First Minister. Nothing, of course, could be better designed to propel Scotland out of the UK than this constitutional double whammy.

The Conservative Party is now probably a greater threat to the continuance of the UK than the SNP. You think that's an exaggeration, but consider: the SNP administration in Holyrood has been sticking pretty solidly to the terms of the devolution settlement. It hasn't declared UDI, tried to seize Scottish oil, or opened negotiations with the EU on introducing the euro. It is currently trying to cope with the tightest budget since 1999 and preparing to dump a lot of its manifesto pledges.

It is behaving, in other words, like a responsible provincial administration, rather than a provisional government of the Independent Republic of Scotland.

Of course, in his conference speech yesterday, Alex Salmond insisted that everything he does in office is being done to "forward the case for independence". But a less Braveheartish address could scarcely be imagined. Not only did it avoid triumphalism, it avoided passionate nationalist oratory. The First Minister even offered - shades of Tony Blair - to lead a "coalition of the willing", of all parties in Scotland who are committed to change.

Alex doesn't make boring speeches for no reason, and one suspects his consensual and downbeat address had been designed to contrast, in its very moderation, with the attacks being made on Scotland by the Conservatives in the London press. Or maybe he just had an off-day. Whatever, the point is that the SNP realises full well that the Scots are in no mood for radical constitutional change right now; they're enjoying the Holyrood show too much.

The SNP has demonstrated just how much power is already devolved. The Scots will not go to the lengths of formally leaving the UK, and setting up the apparatus of an independent nation state, unless they are forced into it. This is why the Tory rhetoric is so risky. English voters might take it seriously and indulge in punitive, cross-border raids, led by a metropolitan press which seems to think that lorry-loads of pound notes are being trundled up the M6 to be dumped in Holyrood.

By fanning the flames of English grievance, and legitimising the "lazy Scots" chauvinism of the Sun's Kelvin MacKenzie, David Cameron risks damaging relations between Scotland and England precisely at the moment when the threat to the Union is subsiding. And he is doing exactly what he accuses Alex Salmond of doing.

It may seem like good knockabout in Westminster to tease Gordon Brown about his Scottishness, and call for an English Grand Committee that would deal with "English" legislation. But if Malcolm Rifkind, author of this putative answer to the West Lothian Question, is serious, and this body is given legislative powers, then the only destination must be a defacto English Parliament sitting in Westminster. The sight of Scottish MPs being locked out of the House of Commons, even for constitutionally legitimate reasons, would be highly provocative. It is bound to lessen Scotland's identification with Westminster. The one person who would welcome it, of course, would be Alex Salmond, who has called for Scottish MPs to stop "interfering" in English affairs.

It may be that constitutional disengagement is now an irreversible process, and that Scotland and England are heading for the velvet divorce courts. However, it isn't in anyone's interest, surely, for Scotland and England to start resorting to the iron fist. Yet it is only by wilfully misrepresenting the state of financial relations between Scotland and England that the Conservative leader can claim that Scotland gets special treatment.

No way does the Barnett formula allows Scots to dip their fingers in English pockets to pay for freebie services. Barnett is designed to reduce Scotland's relative advantage in spending over time and it has been doing precisely that. With a vengeance now that Gordon Brown has turned off the public spending taps. Any new spending commitment by the Scottish Government - such as free prescription charges - has to be paid for by economies elsewhere in the "block". The whole point about devolution was to allow Scots to set their own priorities, and that's what the SNP has been doing.

There are very good reasons why per capita spending tends to be higher here, and it has nothing to do with special treatment. It simply costs more to provide services to people in remote areas. Scotland has one-third of the landmass of the British mainland and one-tenth of the population. But even setting geography aside it is ludicrous to paint Scotland as a burden on the English taxpayer when North Sea oil is pumping tens of billions into the UK treasury and equivalent billions are being spent on London projects such as Crossrail and the Olympics.

As for the new Tory solution to the West Lothian Question, the idea as I understand it is for an English Grand Committee to vote on Bills certified by the Speaker as uniquely English, like the Higher Education Bill that introduced top-up fees in England. But that particular Bill contained numerous clauses that affected Scotland, and had financial implications for the funding of Scottish higher education. Even Tam Dalyell, author of the West Lothian Question, set aside his self-denying ordinance and voted on it.

There's nothing wrong in talking about English affairs, but voting would raise all sorts of anomalies in a unitary parliament. Under the Rifkind scheme, the House of Commons as a whole would have the final vote on "English" Bills, but it would be expected to accept the will of Scottish MPs - much as Westminster is expected to endorse legislation passed by the Scottish Parliament. This would effectively create an English Parliament. And that would require a formal disaggregation of the UK into a federation, like Canada, with separation of powers, regional legislatures and a new UK-wide level of government to handle defence, foreign affairs etc.

Somehow, I don't think English public opinion is ready for that. The SNP would be ready, though, and eager to point the way. I think it would be largely content with a federal Scotland, with wide economic powers and constitutional autonomy under the crown.

Sometimes it seems as if there is an unstoppable momentum towards the deconstruction of the UK. Maybe we should just get on with it.