Andrew Duff is MEP and constitutional affairs spokesman for the Alliance of Liberals and Democrats for Europe (ALDE) in the European Parliament.
President Barroso's intervention in the debate about the future of an independent Scotland in the EU has made the point, forcefully, that nothing is certain other than that the situation is wholly without precedent and mightily complex. Mr Barroso is right to point out that Spain will be a reluctant party to any Scottish separatist negotiation because of Catalonia. The same applies to Cyprus and Greece because of the threat of recognition of the Turkish Republic of North Cyprus. Belgium, with its tetchy Flemish nationalists, is unlikely to be overjoyed.
The Scottish government leads us to believe that a liberated Scotland would not have to apply to join the EU under the provisions of Article 49 of the Treaty on European Union as if it were a third-country candidate. Alex Salmond, Scotland's First Minister, hopes that an ordinary revision of the EU treaties under Article 48 would suffice.
The controversy over treaty base is both interesting and important, although it is crystal clear that no matter which legal route is eventually agreed, the practical result will be the same: unanimous agreement by all 28 member states followed by ratification of that agreement by the 28 plus 1.
In any case, what is largely overlooked is that the first, preliminary phase of the renegotiation will be subject neither to Article 48 (full-blown treaty revision) nor 49 (accession de novo) but will be governed, rather, by the spirit of Article 50, the Union's new secession clause, usefully inserted by the Treaty of Lisbon in order to provide a departing state with the framework for its future relationship with the Union.
In the event of a Yes vote in the referendum on 18 September, the process of the internal demolition of the United Kingdom will start. In accordance with the procedures suggested in Article 50 TEU, the British government will have to inform the European Council of the dramatic news.
The European Council at its October meeting will no doubt then invite the European Commission to come up with an Opinion about what should happen next. The Commission's Opinion will make a recommendation as to the most appropriate legal base(s) for the conduct of the negotiations on the new arrangements, both transitional and final. The Council will then adopt a decision authorising the opening of negotiations and mandating the Commission to conduct them. The European Parliament will exercise its right to be consulted. And at some stage an application to the European Court of Justice for a preliminary ruling on whether the chosen procedures are compatible with the Treaties cannot be excluded (and may even be welcome).
If the rupture takes place in hostile circumstances the EU negotiations will surely be lengthy, and London can be expected to have the support of several revanchist allies. Nevertheless, even if fraught and protracted, the negotiations will conclude at some stage with Scotland emerging as the 29th member state of the Union.
The legacy of having been within the EU for over forty years matters. European integration is not simply a matter of inter-state relations: the Scottish people are EU citizens and will remain so, and it is in everyone's interest that the acquis communautaire, that corpus of EU law which applies now to Scotland because of its membership of the United Kingdom, will continue to apply throughout as well as after the hiatus.
Happily, the EU treaties and the Charter of Fundamental Rights oblige its member states and its institutions to cooperate sincerely in the spirit of solidarity, not to discriminate on grounds of nationality and to respect domestic constitutional structures.
Beyond these steps, the situation will not be clarified unless and until both the UK and Scottish governments spell out in detail their negotiating positions. The critical decision for Scotland is the currency.
Will Scotland seek to inherit the British derogation from the single currency (Protocol 15)? If it does so, will the rest of the EU agree? Strictly speaking (and why not?) as a member state of the Union Scotland will be expected to adopt the euro as and when it fulfils the Maastricht convergence criteria, according to the ordained timetable.
We can only gauge Scotland's progress in this regard once we know the extent of its legacy debt, courtesy of the UK. But why Mr Salmond would prefer to stick with the pound sterling instead of pitching into the euro as soon as possible, I cannot say. One may doubt, as Mark Carney, Governor of the Bank of England, has done that Scotland could truly claim to be independent if its monetary policy and fiscal disciplines were to continue to be set in London.
The deeper truth, of course, is that Scotland in the EU will be no more or less 'independent' than any other member state. In the EU, interdependence is the name of the game. 'Scottish independence' is a powerful slogan: the reality will be somewhat different whether it tried to stick with sterling or agreed to embrace the euro. As Ireland has found, although liberated from Whitehall, its autonomy under the terms and conditions of EU economic and monetary union is strictly conditional on decisions taken in Frankfurt and Brussels.
Beyond the question of the single currency are the UK's plethora of other opt outs and exceptions which are governed by Protocol 20 on Schengen, Protocol 21 on justice and home affairs, and Protocol 30 on the Charter of Fundamental Rights. One can see that the common travel area of the British Isles should stay. But why the Scottish parliament and courts would wish to marginalise themselves like the English from the development of mainstream EU common policies in terms of immigration and asylum, the administration of justice, cooperation of police forces and the like is not self-evident.
After the question is settled of how 'British' Scotland wishes to be, there will still be real and somewhat tough negotiations between London, Edinburgh and Brussels about the number of MEPs each state will elect and about both the actual and relative size of their budgetary contributions.
Finally, one should note that the Scotland question will not be taken in isolation, and that the new EU arrangements for a non-UK Scotland will not be based on things as they are now. The European Union is changing fast. Over the next five years the eurozone is bound to construct a fully-fledged banking union and deepen its fiscal integration.
These reforms will require in any case a constitutional Convention whose likely timetable will start after the British general election in May 2015 and finish after the French presidential elections two years later. At the same time, the UK Conservative Party seems strangely determined to loosen the ties that bind the UK to the EU in time for a British referendum in 2017.
To be fair to the referendum voters, not only Alex Salmond and the Scottish nationalists but also David Cameron and the English nationalists must spell out clearly the catalogue of demands that they each intend separately to perpetrate on the rest of the European Union.