The struggle for independence in the two regions has triggered a multitude of questions at the European level.
Most notably, legal experts are divided as to whether a breakaway region should be automatically granted EU membership status in the case of a 'Yes' vote or whether a new accession procedure needs to take place.
Autonomy inside or outside the EU?
According to Yves Gounin, a French state advisor, the answer is not simple.
On the one hand, the willingness of these regions to be fully sovereign while denying their past obligations is an argument in favour of restarting the accession procedure from scratch.
But the existence of international treaties and the protection of individual rights leads to a full transfer of obligations from the past states - Spain and the UK - to Catalonia and Scotland.
The Vienna Convention of 22 August 1978 brings a few answers for the EU. Even though neither Spain nor the UK has ratified the convention, article 34 is often mentioned in relation to the issue: "Any treaty in force at the date of the succession of States in respect of the entire territory of the predecessor State continues in force in respect of each successor State so formed.”
These states’ links to international treaties depend on the institutional rules of each constitution. The UN for example treats the issue differently in its Charter, since a secessionist country cannot remain a UN member, the Charter says.
The European Commission shares the UN’s opinion. “If part of the territory of a Member State would cease to be part of that state because it were to become a new independent state, the Treaties would no longer apply to that territory,” said EU Commission President José Manuel Barroso in 2012.
Scotland well on the way
Meanwhile, separatists in Catalonia and Scotland are busy making preparations for their independence referendums.
Scotland appears the most advanced. The Scottish National Party (SNP) has pushed for autonomy since 1970. In 2012, the SNP’s leader, Alex Salmond, and the British prime minister, David Cameron, signed the Edinburgh Agreement, which foresees a referendum to be held on 18 September 2014.
Voters will have to answer the question along the lines of the already proposed: "Should Scotland be an independent country?"
A week before the signature of the Edinburgh agreement, a poll conducted for Scottish newspaper 'The Herald' reported that 28% of the population was in favour of independence. Even though separatists are more numerous today, many remain undecided.
The SNP published a white paper on the issue, deemed “the most detailed document ever written in favour of a country’s independence”, by the deputy prime minister, Nicola Sturgeon. The aim of the book is to shed light on the benefits and the changes that independence will bring.
Scotland is already largely independent. It has its own parliament and a decentralised government which handles different sectors such as health, education, environment and police. But defence, foreign affairs and economic policy are still under London’s control.
Strong support in Catalonia
In Catalonia, public opinion is more resolutely in favour of independence. A survey conducted in February 2013 revealed that 52.3% of Catalans are in favour of severing ties with Spain. And 47.4% say they would still be in favour if that meant being excluded from the EU, according to cadenaser.com.
The problem is that the Spanish constitution does not allow any of the regions to organise a vote or referendum over national sovereignty matters.
Artur Mas, the head of Catalonia's regional government, did not bother about such legal considerations and shocked Spanish authorities last December when he decided, together with a majority of his regional parliament, to hold an independence referendum on 9 November 2014.
Catalans will have to answer the following question: “Do you want Catalonia to be a state, yes or no?" If the answer is positive, a second consultation will be organised to ask: “Do you want this state to be independent?”
Separatist aspirations in Catalonia have tended to progress among public opinion, as illustrated by the numerous demonstrations held over the past years. On 11 September 2011, a majority of the 1.5 million people marching on national Catalan day were in favour of independence.
Two years later on the same date, 1.6 million people formed a 400km human chain to demand an independence vote.
Separatist chose 9 November “in order to give state institutions some time”.
But feelings remain contradictory. The president of the European Council, Herman Van Rompuy, said he was “confident” that Spain would remain a unified state. Mariano Rajoy, the Spanish prime minister, shares the same opinion. In 2013, he said that if Scotland decided to be independent, it would need to request accession to the EU.
That question may help the undecided make up their minds as they cast their ballot.