I HAVE a confession to make.

I agree with Gordon. Gordon Brown the former Labour Prime Minister, that is. I agree with his solution to the Scottish question: federalism. The old centralist, sovereign UK is past its sell-by date. In his latest book and recent speeches the godfather of Scottish Labour says there should be a "declaration of sovereignty" for Holyrood so that the UK can be reconstituted as a new multinational state under a written constitution with radical devolution of economic responsibility to Scotland. This is what I call in my book Road to Referendum, "Independence in the UK", a phrase originally coined by the late Donald Dewar.

Where I disagree with Gordon is in this: there is not the remotest chance of this federal reconstitution of the UK ever happening.

Now, I know independence in the UK sounds like a contradiction in terms, an oxymoron. That's often the way with constitutions - look at the EU: a semi-sovereign union of sovereign countries. But the one thing we know for certain about the independence debate is that the vast majority of Scots (around 71% in the most recent poll from the British Election Survey) think federalism is the best option for the UK. It's sometimes called devo max, but no one is in doubt about the general idea.

This stands to reason. Geography is destiny. Locked together on this small island off the coast of Europe, Scotland and England are condemned to co-operate on a whole range of policy issues from marine conservation to broadcasting, monetary union to immigration, and renewable energy subsidies to non-nuclear defence.

On day one after independence, a multitude of cross-border bodies would have to be set up to manage these issues. Given the asymmetrical nature of British geography (the demographic and commercial dominance of England) there will always be a case for there to be some form of democratic representation for Scotland at federal level, or UK level, where many of these key decisions affecting Scotland will be made, even while the vast majority of economic and tax policy is handed to the Scottish state. The countries in the EU are independent but they still send elected representatives to the European Parliament to represent their interests at the centre.

So there is a compelling logic to federalism. But there are two massive and insurmountable problems. First, Scotland will not have an opportunity to vote for federalism in September because it will not be on the referendum ballot paper. Secondly, there is no scintilla of a chance of federalism being introduced by Westminster of its own volition. Look at the plan put forward by Mr Brown's party in Scotland for "more powers". Whatever it is, the Lamont plan for devo more isn't a blueprint for federalism, or anything like it.

Westminster has not the slightest intention of reconstituting the UK as a federal country with a separation of powers, an English parliament, regional parliaments, fiscal disaggregation and so on. England doesn't want an elected head of state; nor does Scotland. The UK political establishment had an opportunity to move to federalism by using the reform of the House of Lords to turn it into a senate. It passed. Anyway, there's no guarantee even that the "more powers" promised by the Unionist parties on Edinburgh's Calton Hill will come to pass. There is no common programme, despite the banners placed with unconscious irony on the unfinished monument called "Edinburgh's Disgrace".

This wasn't a united front on devo plus; it was an agreement to disagree. Labour's offer of 5 per cent of income tax is nugatory; its call for a top rate that can go up but not down, fiscal nonsense. The Conservatives' offer on income tax is radical for them, but a long way from fiscal autonomy. The Liberal Democrats have been advocating federalism for more than 100 years, but not once did it appear in the discussions when they went into coalition with the Tories. The will is absent. People in England don't want an English parliament. They're quite happy with Westminster. Nor do they want to have a written constitution and all that legal stuff, codifying rights and balancing powers. Very unBritish. The British way is to leave it all to whomever dominates the unitary sovereign parliament to decide what the UK constitution actually means. That's not going to change.

The idea that, by voting No, Scotland will persuade this big country, which has a lot on its mind with the EU and immigration, to press ahead with radical constitutional reform is ridiculous. Scotland really isn't on England's radar. Even attempts to whip up antagonism toward Scotland over issues such as the Barnett Formula and the West Lothian Question have repeatedly failed because English people really don't care much if Scots get a few pounds more in public spending.

To understand Westminster's attitude to Scotland, you only needed to listen to the former Conservative Prime Minister, John Major yesterday. His answer to the Scottish question is that Scots should jolly well pipe down and realise when they're on to a good thing. And if they don't, heaven mend them. Every remark by the former Prime Minister was prefaced by a silent "how dare you".

Independence is primarily of interest because it will mean the end of Britain's nuclear deterrent, an admirably frank admission that weapons of mass destruction will not be relocated to England.

The idea that politicians like Mr Major are prepared to plunge the UK into a radical programme of constitutional reform to please Scotland is not credible. The only concrete constitutional promise in the Scottish Conservatives' recent Strathclyde Report was to implement the McKay proposals removing the voting rights of Scottish MPs on nominally English affairs.

The inconvenient conclusion is that Scotland will have to go for federalism in one country, another unavoidable oxymoron. Scotland may have to assert its autonomy and redefine the limits of Westminster sovereignty by making the only declaration of sovereignty that actually means something. As former Labour First Minister Henry McLeish suggested at the Economic Development Association conference yesterday, Scotland will have to leave the UK to rejoin it on different terms. Mr McLeish didn't say he was voting Yes to independence but his body language made it clear he wasn't minded to vote No.

He says he is conflicted precisely because he sees how some Labour colleagues, like Mr Brown, have journeyed to federalism. However, he cannot see any prospect of the party in the UK under Ed Miliband or anyone else adopting such constitutional radicalism.

Anyway, the way the opinion polls are going, Labour will not be in government in 2015. Then Britain will be plunging into its own constitutional crisis as it votes on whether or not to remain in the EU. It's clear that the UK is on its way out of the EU. The only question is whether Scotland goes with it.