The ECJ legal adviser’s opinion on Article 50 makes it easier for MPs to vote for another Brexit referendum

Analysis: If the European court follows this opinion, it would mean a referendum decision to remain in the EU – under existing terms – could be implemented straight away, as John Rentoul explains

Can the deal be undone? (AP)

The European Court of Justice is likely to rule that the UK has the right to cancel its notice of intention to leave the European Union. The court’s advocate general this morning issued an opinion to that effect, and the court usually follows such advice.

If confirmed, this would make a new referendum easier because a vote to remain in the EU could be implemented straight away – and our membership of the EU would continue under the existing terms, the UK rebate on contributions included.

However, the UK government would still have to apply for an extension of the Article 50 deadline so that it could hold a referendum in the first place – and that would still need the unanimous agreement of the EU27 countries.

Some enthusiasts for a second referendum might think that the ECJ’s likely decision would allow the UK to cancel Brexit and then hold the referendum. But that would mean, if the vote were for Leave again, that we would have to start the Article 50 process all over again. Which might fall foul of the advocate general’s opinion, which says that revocation of Article 50 notice is allowed provided it “does not involve an abusive practice”. Revoking and invoking our notice might be seen by the ECJ as precisely that: an illegitimate negotiating tactic.

If the UK asks for more time to hold a referendum, the EU27 are highly likely to agree to an extension to the timetable.

So the significance of this opinion is indirect. It makes a possible referendum simpler because it would present a choice between two definite options: Theresa May’s Brexit deal versus remaining in the EU on existing terms.

That would take away one of the arguments against a second referendum, namely that, if “Remain” were on the ballot paper, it would not be possible to guarantee what it meant because – without this legal opinion – we would need to ask permission of the EU27 to stay in the EU. That would probably be granted, but it might be complicated to secure an agreement to that effect before a referendum.

In the next few days, as MPs debate the prime minister’s Brexit deal, the advocates of giving the people the final say can therefore propose a new referendum that seems credible and well defined.

They know that, if the UK asks for more time to hold a referendum, the EU27 are highly likely to agree to an extension to the timetable. They want us to stay and want to make it easy for us to do so.

That was one of the explicit arguments behind the advocate general’s opinion. He said Article 50 ought to be interpreted in a way “which accords with the objective of advancing the process of [EU] integration”. Giving the UK the right unilaterally to revoke notice of its intention to withdraw makes it easier for us to change our mind and stay.

However, that EU law is interpreted in a way that suits the cause of integration – “ever closer union” in the words of the founding treaty – does reinforce the argument of Leavers that the EU will always seek to become a single superstate.