Will the EU and Holyrood votes take place on the same day?
Could the referendum on the UK's EU membership and the Holyrood election take place on the same day next year? Professors Michael Keating and John Curtice give their views.
Has there ever been a referendum on the same day as a parliamentary election?
Yes it has. Prof Curtice, of Strathclyde University, said: "We should remember that back in 2011 the referendum on the Alternative Vote was held on the same day as the Scottish parliamentary election." The academic added that people were "not terribly interested" in how the House of Commons should be elected and therefore holding the two polls together was not politically controversial.
Is it likely the Holyrood and EU votes would coincide?
Both professors, speaking to BBC Scotland's Good Morning Scotland programme, say it is unlikely. Prof Curtice said: "There are two arguments as to why it probably won't happen.....
- It is pretty likely that the Conservative Party is going to be divided over the referendum. Anybody who has listened to Owen Patterson, the former environment minister, or John Redwood, the former cabinet minister and our commissioner in Brussels, Lord Hill, would reckon that these are not people who are on the same page. Therefore, the Conservatives will not be wanting to fight elections - not only in Scotland, in Wales but the London mayoral contest and local elections in England - at a time where members are going to be on different sides of the issue.
- Secondly, it is perfectly clear that this referendum is going to be a big gig. Do you really want to mix together what will be important elections for Scotland, for London, for Wales, and which in themselves may be important for the future of the union, at the same time as this crucial issue with the European Union?"
What have politicians being saying?
Prime Minister David Cameron is keen to have the referendum "as soon as possible", but he has not said what date he would prefer. During the general election, the Conservative Party pledged to hold the vote before the end of 2017.
Acting leader of the Labour Party, Harriet Harman, told the BBC's Andrew Marr show that she did not want to see the referendum at the same time as the Holyrood election. She explained: "It is a big constitutional issue on its own and needs that separate consideration."
The SNP's former leader Alex Salmond, in an interview with the BBC's Newsnight, said that although the referendum should be sooner rather than later, he believed putting it with the Holyrood election could lead to confusion. He added: "If you think this is important then it is important enough to stand on its own."
Prof Keating, from Aberdeen University, said the timing of the referendum was an important one for Labour and the SNP.
He explained: "Both Labour and the SNP will be fighting each other furiously in the Scottish election but be on the same side as the European election so that would cause great difficulties for them and their campaign organisations and great confusion for the electorate."
What else might determine the referendum date?
Ahead of the vote, Mr Cameron will attempt to re-negotiate a new deal for a UK within the EU.
Prof Keating, of Aberdeen University, said it appeared "pretty unlikely" that the prime minister would be able to get his negotiations completed within less than a year. He added: "This will then have to go to the Westminster parliament and a proposition put to the electorate, unless Mr Cameron is going for a very quick fix, for minimal change, then he is going to require more than a year.
"If he does do a very minimal cosmetic change, say fiddling around with benefits for EU migration, but not doing anything else, then he has deep problems with his own party, so I would expect this to take more than a year."
Will 16 and 17-year-olds be able to vote?
In the Scottish independence referendum, a one-off ruling ensured that 16 and 17-year-olds could vote in the historic poll. However, Prof Keating said: "I don't think it will happen for this election."
But he added: "Votes for 16 year olds is going to come, most of the parties are in favour of it, the Conservative will probably come around. There was a very positive experience in the Scottish referendum with these young people getting engaged and turning out to vote."
So, who will get a vote and why?
Downing Street has indicated that most EU citizens living in the UK will not get a vote in this referendum, unlike the Scottish independence referendum.
However, Irish citizens in the UK, residents from two other EU nations Malta and Cyprus and Commonwealth citizens will be eligible.
Prof Curtice said: "I don't think we should be surprised, if you look at the franchise used for the Alternative Vote in 2011, which again was about the future of the House of Commons elections, we used the parliamentary franchise."
Prof Keating added: "As for EU citizens, the Scottish referendum was peculiar because they used the franchise for the Scottish Parliament which happens to include EU citizens. But in other EU counties, where they have had referendum, it is only the nationals of these countries that are allowed to vote."
- Prof Michael Keating and Prof John Curtice were interviewed by BBC Scotland's Good Morning Scotland by presenter Andrew Kerr on 26 May, 2015.