I don't know about Tantric sex, but the Prime Minister is certainly a teaser.

Last week he informed hungry hacks at a Westminster press lunch that he had postponed yet again his long-awaited speech on a referendum on Europe. He said that, like Tantric sex, it would be worth the wait, though I'm not quite sure for whom. Perhaps he is suggesting that the opposition, or the EU, will be shafted. Or could it be Scotland?

Scottish debate on Europe has been depressingly parochial. For weeks, commentators and unionist politicians have been blasting the SNP for not being able to guarantee that Scotland would gain automatic entry to the European Union after independence. What the myopic chatterati have failed to grasp is that the UK is moving rapidly away from the EU and, under the present constitutional arrangements, is likely to take Scotland with it – at least if the majority of Tory MPs in Westminster get their way.

Conservative opinion on Europe has changed out of all recognition in the 20 years since the Tory Prime Minister, John Major, faced down his rebels and ratified the Maastricht Treaty creating the European Union. That was when it was still possible for a Tory PM to say that they wanted Britain to be "at the heart of Europe". Not any more, they don't. They are all eurosceptics now. It is extremely rare to hear anyone in the Conservative Party having a good word for Brussels, which is now universally condemned as a parasitical bureaucracy presiding over a basket-case currency that will shortly collapse.

David Cameron is a pragmatist, and doesn't want to cut economic ties with Europe, but he is under increasing pressure to hold a referendum – and not just from his parliamentary party. The UK Independence Party is snapping at Tory heels in southern constituencies, and the UK press, led by the Daily Mail and The Sun with their five million readers, is increasingly europhobic.

According to YouGov, a clear majority of English voters say they either want to leave the EU or renegotiate the terms of British entry. The Labour leader Ed Miliband has turned trappist on Europe, because he doesn't want to be on the wrong side of public opinion, and is likely to back a referendum on Europe after the next General Election. The Liberal Democrats have also called for a referendum on British membership.

Cameron is expected to say this: Britain will make a series of proposals for renegotiation to Brussels along the lines of "back to the Common Market". In other words, Britain would explicitly be opting out of the European Union, and rejecting its right to legislate on UK internal affairs. This will be a momentous step. It will almost certainly be rejected by the European Union because there is no "Common Market" left to join. Britain would have to opt out of the EU altogether and seek status such as Norway, which is part of the European Economic Area.

But Norway, while in many respects a favourable model for Scotland, is not going to appeal to Tory eurosceptics. This is because Norway adopts almost all of the regulations that issue from the Brussels on the single market but has no say in shaping them. It also pays more to Brussels than proper member states.

But if Britain doesn't join the EEA, then it really would be out in the cold, and would have to negotiate on very difficult terms for access to the 500 million-strong EU market. Not many people realise that this could mean big tariffs on British exports, especially agricultural ones. Dairy products have a 55% duty. Of course, Tories believe that freedom is more important than the price of cheese.

What does all this mean for Scotland? Well, it means that the run-up to the Scottish referendum on independence IN Europe will likely be dominated by debate about a referendum on independence FROM Europe. Alex Salmond's game plan is that, when the Scottish referendum takes place in 2014, the political landscape of Britain will have changed.

First of all, in the European elections of June 2014, the Tories are expected to come under intense pressure from the UK Independence Party, which came second to Labour in a couple of by-elections last month. This will ratchet up the pressure on David Cameron – and Ed Miliband – to big up their plans for a referendum to be held in 2015 or 2016 on Britain's membership of Europe.

The SNP's critics in the Scottish media, and the unionist parties in Holyrood, will have to confront the awkward reality that, if Scotland remains in the UK, it could very well be taken out of Europe into some netherworld in which Scots would lose their citizenship rights in Europe and would lose EU social protections like the working time directive.

Scotland's university-based technology industries would find that they could no longer co-operate on joint projects in Europe without complex negotiations. Scotland's financial services industry could lose out as Britain becomes remote from the banking and fiscal union that is being constructed in Europe.

Not only that, Scottish farmers would find that they are locked out of vital markets by tariff walls; Scotch whisky could be priced out of some of its most valuable markets; EU workers would no longer be able to come to Scotland to work in Scottish hotels and restaurants. Following the shock of the 2011 census, which showed that three million migrants had entered the UK in a decade, England is almost certain to impose tight restrictions if it leaves the EU. This could deprive Scotland of the young workers it needs to help fund its elderly population.

So the Nationalists believe that the argument in Europe will be going their way by October 2014, and that Scots will see that they should vote Yes to independence to ensure that Scotland remains in Europe.

The Nationalists are content to have the current debate on Scotland's EU membership after independence, even though they are on the defensive, because it at least presumes that Scottish membership of Europe is a good thing in itself. However, they are missing a couple of vital caveats.

First of all, it is not entirely clear that Scots are all that enthusiastic about Europe. Opinion polls on Scottish attitudes have pretty unreliable samples, though the most recent show only marginally more enthusiasm in Scotland for the EU, especially the social protections. The Scottish Government's own research in 2007 into attitudes to Europe found that the number of Scots who wanted to leave or renegotiate amounted to 51% – not far short of the eurosceptic numbers in England.

The assumption in Nationalist circles is that the mere fact that English Conservatives are leading the hostility to Europe will be enough to make Scots rediscover the virtues of the EU. This is probably the case, but cannot be guaranteed.

Also, the Nationalists have always assumed the EU wants Scotland to remain in the community after independence, if only to hang on to fish, oil, renewable energy and our highly educated workforce. However, they reckoned without the intervention of the EU President, Jose Manual Barroso, who seems to be in no mood to welcome Scotland.

Last week, he told the House of Lords that an independent Scotland would become a "third country", that EU Treaties would "not apply on its territory" and that Scotland would have to reapply "just like any new state". The SNP insists that since there is no mechanism for ejecting a member country, Barroso is not entitled to say any such thing. Would five million EU citizens in Scotland be expelled?

Certainly, no constitutional authority in the UK has suggested that Scotland would be refused membership, but negotiating it could take time.The SNP only finally accepted this reality last week, when Nicola Sturgeon, the Constitution Minister, conceded in a statement to the Scottish Parliament that there would have to be tough negotiations over Scotland's non-adoption of the euro, the Scottish contribution to the EU budget and the Schengen agreement on free movement across borders. Like the confusion over the non-existent legal advice on EU membership, this lapse has left the SNP looking as if it hasn't been thinking things through.

Since the EU is a byword for bureaucracy, it doesn't take a genius to work out that there could be delays over Scotland's continued membership. It is possible that, since the rest of the UK would also have to negotiate on issues like its budget contribution, Brussels might be keen to fast-track the process, if only to prevent this being used by British eurosceptic Tories as a pretext for leaving the EU. But clearly this can't be assumed.

We live in an age of uncertainty in which constitutional relations are being renegotiated at all levels. We don't even know if the eurozone will survive another year of the sovereign debt crisis. What we do know is that, if it does, the EU will have to become much more like a federal state, with a central treasury and common tax and spending policies across the EU. It's pretty clear that the UK doesn't want any part of that. Scotland has yet to express its settled will.