SUDDENLY the momentum is building for a UK referendum on Europe.

Indeed it's beginning to look unstoppable. The Tories, the dominant partners in the UK Coalition Government, see their support evaporating at an alarming rate. A lot of it is going to UKIP, the aggressively anti-EU party which is no longer just a fringe organisation in England (it is far less significant in Scotland).

Last week Lord Owen, the former British Foreign Secretary, demanded a UK referendum to allow the British people to decide their future vis-a-vis Europe. He reckoned that as Germany was promoting the idea of a single European government, Britain's voters had to be given the choice of staying in the EU, and joining the eurozone (obviously not a popular move right now) or quitting the EU but remaining in a wider, looser European "community" which would be outside the eurozone.

His intervention was timeous. It reflected a growing, even urgent, mood in England. There is there a growing belief in England that Britain has to prepare to disengage from the potential European superstate that the Germans wish to create. A referendum would be the constitutional device used to legitimise this disengagement, and the demand for such a referendum will, I believe, become irresistible south of the Border. But there is a complicating factor which concerns Scotland.

Obviously the dominant, governing, party in Scotland is the SNP – and the SNP is very firmly pro-European. It envisages an independent Scotland in Europe. It believes that this vision can and will be acceptable to the Scottish people in the referendum on Scotland's future which is due to be held in the autumn of 2014. But how exactly will the role of Scotland in Europe be presented to the Scottish people?

Suppose there is a UK-wide referendum on Europe shortly before our referendum on Scottish independence. Scots would take part in that UK referendum. What would happen if a majority of Scots voted, in Lord Owen's phrase, to "escape the shackles of Brussels"? That is unlikely, but distinctly possible, particularly if the Labour Party was by then committed to leaving the EU as it currently exists. A UK-wide referendum on Europe could have a huge bearing on the later referendum on Scottish independence. It might even leave a key SNP policy in tatters.

Right now Europe is not a problem for the SNP. It's a major and growing problem for both the Tories and Labour. Serious repositioning by both parties on Europe is bound to happen soon. It would be ironic, to put it mildly, if a problem for the two main London-based parties were to have an indirect, but crucial, bearing on the Scottish referendum, and indeed the entire future of Scotland.

David Cameron claims publicly that he wants closer eurozone integration in terms of fiscal and political union because that is the best way, at present, of protecting the European market which is so vital for UK exports. On the other hand, most of his grass roots supporters (and probably him too, privately) abominate the very idea of closer European integration, even it if makes economic sense. So Mr Cameron is caught in a particularly nasty trap.

Labour faces similar difficulties. Under Ed Miliband's thoughtful leadership, the party looks like taking a more hostile approach to the EU. Certainly the appointment of Jon Cruddas MP, a committed Eurosceptic, as Labour's head of policy, points strongly in that direction. Labour, like the Tories, could see a constitutional referendum as the best way forward.

In England there is a growing consensus that the EU, as currently constituted, is not in the best interests of the English. No parallel consensus exists north of the Border. But if there is growing support in England for disengagement from the EU, that could have enormous implications for Scotland. The arrival of an EU-free England might ultimately make an independent Scotland all the more likely. But the process of achieving that EU-free England might create many snares for the SNP.