Europe's highest court has issued an opinion that the Irish High Court was right to postpone the extradition of a suspected Polish drugs trafficker to Poland because of concerns over alleged government interference in the judiciary.

However, this did not mean that no Polish court could not hear any extradition cases and it was essentially up to the Irish court to establish all the facts to see if the accused was indeed able to have a fair trial.

The case relates to Artur Celmer, a 31-year-old Polish national who was sought by the Polish authorities over alleged drugs trafficking offences dating back to 2007.

In May last year he was arrested and jailed in Dublin pending an extradition request by Poland via the European Arrest Warrant (EAW).

However, in the High Court, Ms Justice Aileen Donnelly raised concerns that the alleged undermining of the judiciary by Poland's right wing government could mean that Mr Celmer might not get a fair trial, and that the normal trust between national judiciaries, which underpins the EAW, had been damaged.

The High Court referred the case to the European Court of Justice (ECJ) in Luxembourg.

Today, in a highly anticipated move, the ECJ's advocate general issued an opinion that in this case, the Irish High Court was right to postpone the extradition, but that it had to show that the lack of independence had to be so serious as to destroy the fairness of Mr Celmer's trial.

It was up to the Irish court to determine whether that was the case, and whether it amounted to a flagrant denial of justice.

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The case has been closely watched across Europe, and comes as the European Union has launched a so-called Article 7 case against Poland for what the European Commission calls the "systematic" undermining of the Polish judiciary and the rule of law.

On 20 December, under Article 7 of the EU Treaty, the European Commission asked the EU Council of Ministers, representing member states, to see if the changes to the Polish justice system meant there was a clear risk of a serious breach of the rule of law by Poland.

Advocate General Evgeni Tanchev held that the execution of an EAW had to be postponed if the competent judicial authority found that there was a real risk of a "flagrant denial of justice" on account of any deficiencies in the system of justice of the issuing Member State.

However, there would also have to be clear evidence that the person being extradited was exposed to such a risk.

It was up to the judicial authorities in the processing state, in this case Ireland, to determine whether there was a risk of a fair trial, irrespective of any move to sanction Poland under Article 7.

In order for an extradition to be postponed, the Advocate General held, there had to be a real risk, not of the breach of the right to a fair trial but of a flagrant denial of justice.

The Advocate General found that any limitations to the principle of mutual trust between member states in executing an EAW had to be interpreted strictly.

The right to a fair trial could be subject to limitations, so long as those limitations respected the essence of that right.

As such, the executing judicial authority was required to postpone the execution of an arrest warrant only if there was a real risk of breach of the essence of the right to a fair trial.

Furthermore, it was up to the national court processing the warrant to decide whether Mr Celmer, named in court documents as LM, had demonstrated in what way the deficiencies in the Polish system of justice, assuming that they were proven, would prevent his case from being heard by an independent and impartial tribunal.

The decision by Ms Justice Donnelly to refer the EAW to the Luxembourg court triggered strong criticism from the Polish authorities.

In a submission to the ECJ, the Polish government said the courts of one member state had no right to judge those in another, and suggested that the Irish legal system itself had been politicised.

Today's opinion comes ahead of the full judgment.

In 80% of cases the final ruling is in line with the Advocate General's opinion.