I mentioned earlier that I had contacted lawyers whom I had read were considering the legality of the Scottish Referendum in European law.
I have now received a gracious and comprehensive reply, below, from Matrix Chambers.
".......... I can confirm the legal position is presently as follows:
(1) Because of legal uncertainty as to whether the Scottish Government/Scottish Parliament could legally (i.e. within the confines of the powers conferred under the Scotland Act 1998) the UK Government found it politically expedient to agree with the Scottish Government to amend the Scotland Act to put the matter beyond doubt and expressly give the Scottish Parliament a time limited power (until 31 December 2014) to organise a referendum on independence.
(2) This Edinburgh agreement left it to the Scottish Government/Scottish Parliament to pass legislation determining the franchise for this referendum.
(3) The Scottish Parliament has power to legislate only in and for Scotland. In passing the franchise issue to the Scottish Parliament in effect the UK government made a decision that only Scottish voters, rather than any voters in the rest of the UK could have any say in the independence referendum.
(4) There are in effect two established voting registers for elections in Scotland: general elections to the UK Parliament; and local government elections for local authorities and elections to the devolved legislature.
(4) For general elections to the UK Parliament, there is an entitlement to vote given to all British, Commonwealth and Irish citizens residing in the UK at the time of the election. Additionally however UK citizens who were formerly resident in the UK but have moved aboard retain the right to vote in general elections for period of 15 years after they ceased to be resident in the UK.
(5) For local government elections, there is an entitlement to vote given to all British, Commonwealth and Irish citizens and all other EU citizens residing in the UK at the time of the local election. This right of EU citizens to vote in UK local elections derives from the Maastricht Treaty and is enshrined now in Article 20(2) of the Treaty on the Functioning of the European Union. Crucially however there is no retention of any voting rights in local elections for UK citizens who were formerly resident in the UK.
(6) The Scottish Government decided that the franchise for the independence referendum would follow the local government franchise. The result is that all British, Commonwealth and Irish citizens and all other EU citizens residing in Scotland at the time of the referendum get to vote on Scottish independence. No UK national who is not resident in Scotland will get a vote in the referendum.
(7) Had the Scottish Government chosen instead to follow the model for UK general elections, then they would have referendum from which other EU nationals were excluded from the vote, but in which in principle UK nationals who had been resident in Scotland up to 15 years before the referendum would have a vote in it.
(8) It should be noted that it was within the power of the Scottish Parliament to vary the existing models for the franchise as they thought fit. Indeed they did so by reducing the voting age for this referendum from the usual 18 down to 16.
(9) The use of whether Scottish born expats - whether living elsewhere in the UK or aboard should get the right to vote was barely discussed in the Parliament when the franchise was being decided upon. This has now become an issue however because the Scottish Government now proposes (which was not known at the time the franchise was fixed) the following in its proposed post-independence interim constitution, a new status of Scottish citizenship which will be afforded automatically and unilaterally by an independent Scotland on "all those who, immediately before Independence Day, hold British citizenship and either— (i) are habitually resident in Scotland at that time, or (ii) are not habitually resident in Scotland at that time but were born in Scotland"
(10) So Scottish born expats are going to be directly affected by the result of the referendum as regards their citizenship status but are being given no say in whether or not there should be an independent Scotland of which they will automatically become citizens.
(11) In terms of the legal issues this might raise that could be enforceable before the courts, the only argument Mr O’Neill could come up with is one based on EU law. The principles of EU law are that no individual should be discouraged from exercising their free movement rights within the EU to travel and take up work in other Member States. If an individual who leaves to take up residence in another Member State is by that very move immediately and automatically deprived of his rights to vote in crucial issues within his home member State, he may be deterred from exercising his free movement options. The deprivation of the right to vote in the independence referendum for all those who would or have exercised their free movement rights would seem therefore to be a penalty of disenfranchisement which is consequent upon the exercise of free movement rights and so is contrary to EU law.
(12) Despite public interest in this issue, there was no-one willing to fund an action before the national courts based on this EU law argument. Accordingly all that has happened is that a formal complaint has been made to the European Commission on the issue. A formal complaint was sent to the European Commission about this, but Mr O’Neill doubts, however, if any decision will be forthcoming from the Commission on the issue before the referendum takes place on 18 September."