Attorney General for Northern Ireland John Larkin QC. Photo Charles McQuillan/Pacemaker Press

In a characteristically blunt speech today, Mr Larkin was repeatedly scathing about the actions and unaccountable nature of the EU’s supreme court, the European Court of Justice in Luxembourg, which rules on questions of compliance with EU law.

The Attorney General’s comments came just hours after Prime Minister David Cameron was due to fly to Belfast to make the case for the UK remaining within the EU.

Speaking at a conference in Belfast organised by the Centre for Democracy and Peace, Mr Larkin delivered a withering assessment of the Luxembourg court.

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He contrasted it with Louis IX who “considered himself as accountable only to God; the Court of Justice of the European Union considers itself as accountable to no one. It is one thing for kings to act as judges; it is quite another for judges to act as kings.”

As Mr Larkin spoke, a former judge of the Luxembourg court who was a fellow speaker at today’s event, Judge Fidelma Macken, listened.

Mr Larkin began by saying: “I think that not only would the protection of fundamental rights and liberties not be diminished by a United Kingdom withdrawal from the European Union, but I think there is a prospect that the protection of fundamental rights and freedoms would actually be enhanced by such a withdrawal.”

He added: “Those of us who are familiar with the distinction between the Council of Europe and the European Union will realise that nothing is going to change [in the event of a UK withdrawal from the EU].

“The United Kingdom will still be a member of the Council of Europe, will still be bound by the European Convention on Human Rights...and will still be subject to the terms of the Human Rights Act 1998, so nothing is going to change in terms of the protection provided by the European Convention.”

Mr Larkin acknowledged that his argument that fundamental freedoms could actually be enhanced by leaving the EU “was going to seem a little more contentious”.

The Attorney General said that at the heart of the issue was the question of “how we are to be governed”. He went on: “I think an intellectually honest answer to that question must necessarily acknowledge that the judicial role in the European Union through the Court of Justice, the European Union and therefore in our government is greater than it should be.”

Mr Larkin went on to describe the Luxembourg court as “supremely and unassailably unaccountable” and suggested that a controversial 2014 decision was particularly dangerous.

He argued that the “absolutely astonishing decision” – known as Opinion 2/13 – had been to ward off the “nightmarish” scenario (from the Luxembourg court’s perspective) that the Strasbourg court could hold it to account on human rights matters by ruling that human rights complaints about EU institutions could not be taken to the European Court of Human Rights in Strasbourg.

Describing it as a verdict which is “riddled with errors”, he said it was “one of the most important decisions this century in terms of the constitutional balance of the European Union and the protection of the rights of citizens of the union”.

Yet despite the significance of the judgement, he said that the precedent which it has set could only be overturned by treaty change – something which would require every single EU member state to agree.

“This decision means that a claim that an EU institution has breached a citizen’s rights under any of the substantive articles of the European Convention on Human Rights cannot and will not be litigated before the European Court of Human Rights in Strasbourg because the EU will not be a signatory to the Convention,” he said.

“This removes any prospect of a significant protection existing for EU citizens against abuses of their rights by EU institutions. A citizen of the United Kingdom cannot complain to Strasbourg about an EU human rights abuse.