The Catalan independence movement has received a boost following a European Court of Justice (ECJ) opinion that it is up to the European Parliament, and not the Spanish authorities, to decide whether or not a jailed Catalan MEP should enjoy immunity from prosecution.

An ECJ advocate general has recommended that the immunity enjoyed by Oriol Junqueras, who was elected to the European Parliament in May, but jailed for 13 years in October by the Spanish courts on sedition charges, could not be curtailed simply because he had not signed an oath to the Spanish Constitution.

Spanish judges had ruled that because Junqueras, and two other new-elected Catalan MEPs, had not taken the oath due to their imprisonment, they were technically not MEPs.

However, today the advocate general said once a person is elected MEP they acquired the status of an MEP "notwithstanding any subsequent formality which that person is required to complete, whether under EU law or the national law of the Member State in question."

Advocate general Maciej Szpunar said that because Junqueras had acquired the parliamentary mandate and thus the status of an MEP he is "therefore...capable of benefiting from immunity" from prosecution from the moment he takes up his mandate from the European Parliament.

He said the Spanish authorities "are required to  refrain from any measure which might obstruct the necessary steps of that MEP to take up his/her duties and to suspend the measures which are already in force, unless immunity has been waived by the European Parliament.

Under Article 9 of the European Parliament's protocol on immunity, the Parliament can decide whether to uphold or waive the immunity of an MEP.

Szpunar recommened that Article 9 be interpreted as meaning that it falls to the European Parliament to decide whether it is appropriate to waive or defend the immunity of one of its members.

Two other Catalan leaders, Carles Puigdemont and Toni Comín who are in self-imposed exile in Belgium have launched legal challenges against the European Parliament.

Following today's opinion by the advocate general, the full ruling will be delivered in the coming months.

In 80% of cases, the final judgment reflects the earlier opinion of the advocate general.