The stand-off over Poland and the supremacy of EU law has presented national capitals with an enormous political and legal headache.

That is partly because the issue of primacy is not as clear cut as it could be.

That in itself has been a matter of scholarly debate for some time, and national courts have increasingly tested where the line between EU and national legal primacy can be drawn.

However, the EU now believes Poland is twisting that ambiguity to protect itself against the genuine charge that it has launched a wholesale assault on the independence of the Polish judiciary.

In June 2015, the right-wing Law and Justice Party (PiS) ensured that judges appointed to the Constitutional Tribunal should be elected by the Polish parliament, leading to widespread criticism that the court had been taken over in order to deliver favourable rulings to the government.

Since then, critics say, the takeover has extended to the public prosecutor's office, as well as the Supreme and lower courts.

'The primacy of EU law is not black and white'

According to Aleksandra Kustra-Rogatka, of Nicolaus Copernicus University in Krakow, that takeover was necessary for the completion of Law and Justice's ambitions.

"After the 2015 elections, it quickly became apparent that the government was seeking to subjugate the judiciary. The first target was the Constitutional Court. As the essential constitutional guarantor, if it had remained independent, it would have stood in the way of the undermining of the other parts of the judiciary," she wrote in a paper for the rule-of-law NGO Re:constitution.

In Brussels diplomats say Warsaw is attempting to make the dispute a Poland-versus-EU institutions struggle, when the independence of the judiciary is the real issue.

The charge is that PiS politicised the Constitutional Tribunal, asked it a question about the primacy of EU law, and then got the answer it expected.

"The primacy of EU law is not black and white," says one EU diplomat.

"This is what makes it so complicated. Primacy is a gray area. But the Polish court judgment has made it black and white. And they've gone way beyond grayness. It's stark: 'our constitution is superior'."

Legal experts have suggested that the EU's reluctance to spell out in black and white the primacy issue may come to haunt the bloc in light of the Polish challenge.

"No such principle was enshrined in the 1957 Treaty of Rome, the then European Economic Community's founding document, or in any subsequent EU treaty," wrote European law specialists Stefan Auer and Nicole Scicluna in Politico this week.

"Rather, legal supremacy was established by the European Court of Justice (ECJ) itself, in its landmark 1964 Costa vs ENEL decision. The great success of the EU as a community of law lies precisely in the fact that national authorities upheld that principle for many decades after 1964, despite it never having been expressly endorsed by the EU's member countries."

The question came up again in the 1970s during landmark rulings issued by the German Constitutional Court in what quirkily became known as the Solange I and Solange II cases.

Solange I dealt with the question of export licences under the Common Agricultural Policy (CAP) and whether they breached human rights protected by the German constitution.

The German court effectively accepted the primacy of EU law in this instance "so long as" (hence the title of the case) it didn't breach fundamental protections under German law. In essence, the court accepted that the ECJ itself was asserting a role in protecting the fundamental rights of EU citizens.

Solange II upheld this judgment by saying that: " long as the European Communities [Solange die Europäischen Gemeinschaften…] and in particular the case law of the European Court, generally ensure an effective protection of fundamental rights as against the sovereign powers of the Communities which is to be regarded as substantially similar to the protection of fundamental rights required unconditionally by the [German] Constitution."

This is how things stayed - until the early 2000s.

Following a very bad-tempered leaders' summit in Nice in 2000, and ahead of the big bang enlargement of the EU in 2004, it was agreed that Europe needed an ambitious rethink on how its powers and democratic accountability should be configured.

The Convention on the Future of Europe was launched in February 2002 to create a new EU constitution. It brought together 102 representatives of national and accession governments, politicians, trade unions, stakeholders, MEPs and EU institutions.

One of the most sensitive issues was the primacy of EU law. National governments had quietly accepted that if it was to function, then as a rules-based body the EU would have to have primacy over national law when it came to delegated competences.

However, ahead of an intergovernmental conference that would sign off on the Constitution, putting this into black and white worried a number of member states, including the UK and Portugal.

"Although in the Convention the article on primacy was accepted as part of the overall package, the UK in particular remained uncomfortable with it being so obviously flagged up," wrote Guy Milton, Jacques Keller-Noëllet and Agnieszka Bartol-Saurel in the book The European Constitution: its origins, negotiation and meaning.

"Yet it resisted the temptation to push for a reopening of the article in the Intergovernmental Conference, and settled instead for a short declaration which it considered provided the necessary reassurance."

That short declaration was Article 1.6: "The Constitution and law adopted by the institutions of the [European] Union in exercising competences conferred on it shall have primacy over the law of the Member States."

Tension between the ECJ and constitutional courts persisted

Of course, the EU Constitution was short lived, having been rejected in 2005 by French and Dutch voters in separate referenda.

Its replacement was the Lisbon Treaty. EU leaders squeamishly dropped any reference to the primacy question, instead relying on a declaration that pointed to ECJ case law on the issue.

The declaration, in an annexe to the Treaty, states that "in accordance with well settled case law of the [ECJ], the Treaties and the law adopted by the [European] Union on the basis of the Treaties have primacy over the law of Member States, under the conditions laid down by the said case law".

If people were wondering why the primacy issue was dropped as an article and put in an annexe, there was an accompanying legal opinion by the Council (ie, the member states) reaffirming that primacy was a "cornerstone principle" and that its absence from the treaty "shall not in any way change the existence of the principle and the existing case-law of the Court of Justice".

Defenders of EU primacy also refer to Articles 4 and 6 of the Lisbon Treaty which state that the EU shares competence with member states in key areas of the single market, and has competence in areas which "support, coordinate or supplement the actions of the Member States".

However, tension between the ECJ and constitutional courts persisted.

In 2012 the German Constitutional Court examined a complaint that the ECB's purchase of sovereign bonds on the secondary market was contrary to the German law which approved the creation of the European Stability Mechanism (ESM), the EU’s new bailout fund.

Ultimately the court deferred to the ECJ.

But the ongoing challenges gave rise to the notion of "constitutional pluralism". Essentially, the tension between the ECJ and national constitutional courts - and which of the two had the final say - could be resolved through judicial dialogue and mutual tolerance.

But a much more serious challenge came in 2020, again relating to ECB bond purchases. The bank had been buying up two trillion euro in government bonds since 2015, but in 2018 the ECJ judged the purchases as legal.

However, a group of German academics, politicians and entrepreneurs, some of whom were associated with the creation of the soon-to-be hard right AfD party, complained before the German Constitutional Court in Karlsruhe that they were illegal because there had been no democratic scrutiny. Both the ECB and ECJ had acted outside EU law, they said.

On 5 May last year, Karlsruhe delivered a stunning verdict.

While it stopped short of declaring the bond purchases illegal, it gave the ECB three months to justify its actions or lose the contribution of the Bundesbank (an outcome which would have put in doubt not just the bond-buying programme but Germany’s membership of the euro).

Given that it landed in the middle of plans for a multi-billion euro Covid recovery package, the judgement was unsettling. It also cast doubt on the ECB’s fiercely guarded independence.

European Commission president Ursula von der Leyen

The ECJ issued a statement that "the Court of Justice alone - which was created for that purpose by the member states - has jurisdiction to rule that an act of an EU institution is contrary to EU law".

The European Commission president Ursula von der Leyen hinted that Brussels could take legal action against Germany.

However, the judgment was hailed in Poland and Hungary.

"The [German] Federal Constitutional Court has confirmed an obvious fact that corresponds to the long-standing assessment of the Polish Constitutional Court," Sebastien Kaleta, the Deputy Minister of Justice told Die Welt.

This in turn prompted dismay among those who feared that increasingly autocratic member states would delight in the Karlsruhe judgment.

In a syndicated article, co-signed by 22 European law academics, legal experts Daniel Kelemen, Piet Eeckhout, Federico Fabbrini, Laurent Pech and Renata Uitz argued that Hungarian and Polish reaction underscored a real problem, "namely that constitutional pluralism and constitutional identity arguments are prone to abuse by autocrats and their captured courts".

At the time of the judgment Poland was already locked in a dispute with Brussels over the creation of a disciplinary tribunal within the Polish Supreme Court which could sack judges and prosecutors across the country.

In October 2019, the Commission had referred the case to the ECJ. The following April, one month before the Karlsruhe judgment, the ECJ ruled that Poland should suspend the tribunal immediately.

Then in July of this year, the ECJ ruled that tribunal was incompatible with EU law.

A Commission statement said: "The Polish disciplinary regime undermines the judicial independence of Polish judges and it does not ensure the necessary guarantees to protect judges from political control."

While Warsaw signalled it was willing to cooperate, the Commission believed it was backsliding on commitments. On 7 September Brussels asked the ECJ to approve the imposition of daily fines on Poland for not complying with earlier ECJ rulings on the tribunal.

The Commission also started fresh legal proceedings because Poland had not complied with the 15 July ECJ ruling asking it to suspend the disciplinary tribunal.

Things were now escalating.

Polish Prime Minister Mateusz Morawiecki

Put simply, Poland believed that the ECJ did not have the legal right to tell Poland to shut down a tribunal that disciplined judges.

In a letter to EU leaders, prime minister Morawiecki raised the stakes further, warning of a "dangerous phenomenon that threatens the future of our Union", namely that the ECJ was transforming the EU into an entity "that would cease to be an alliance of free, equal and sovereign states, and instead become a single, centrally managed organism, run by institutions deprived of democratic control by the citizens of European countries".

Morawiecki, indeed, was invoking constitutional pluralism. He said the demarcation line between EU competences and national competences was drawn by both the ECJ and national constitutional courts.

National courts "can verify the compliance of EU primary law with their own constitutions, and they have been doing so consistently for many years, even decades," he wrote.

Now, he said, if national courts concluded that ECJ rulings were not binding on member states then that was the case.

In a speech to the European Parliament on Tuesday he went further, accusing the ECJ of "judicial activism" by making "decisions...behind closed doors...without a clear basis in the treaties".

There was strong support for the European Commission to continue to pressurise Poland

Several member states expressed alarm at Morawiecki’s argument, not least that he was taking the EU down a rabbit hole in order to provide cover for the politicisation of Polish courts.

Officials pointed out that the national courts Morawiecki had referred to had looked at the primacy issue only on very narrow grounds, and that the German court had never questioned the overall primacy of EU law.

"It’s an all-encompassing judgment," said one EU diplomat. "No other court has ever gone that far. The most difficult element of it is that the judgment has been issued by a court that is now seen as politicized. Quite a number of the judges were appointed by the government. If it was an entirely independent court, and had a legal argument, it might make it a little bit more palatable."

As EU leaders arrived in Brussels on Thursday, the question was how the majority of member states could steer Poland back from its position.

While a group of countries, led by the Netherlands, wanted tough action, it was eventually agreed that a shouting match between leaders would not serve any purpose.

There was strong support for the European Commission to continue to pressurise Poland, but each option is problematic.

The nuclear option is Article 7 of the Lisbon Treaty, which allows for a country’s voting rights to be suspended if there are persistent breaches of EU rules. That requires unanimity, and although the option has been triggered for both Poland and Hungary, each country can rely on the other to veto any definitive punishment.

Under Article 7 an interim step is possible. Four-fifths of member states could declare there is "a clear risk of a serious breach by a Member State of [EU] values".

Again, this is problematic: diplomats believe the threshold of 20 member states would not be reached due to abstentions by eastern and central European countries.

That leaves continued legal action on several fronts, and a move to block EU and Covid recovery funds.

When the €750 billion Covid Recovery and Resilience Fund (RRF) was agreed by leaders last summer, a fierce sticking point was over Poland’s crackdown on LGBT rights. Why should Poland receive some €24 billion in grants and a further €12 billion in loans while simultaneously targeting minority groups, was the argument made by the Netherlands and others.

To get the package over the line, a "conditionality mechanism" was inserted meaning the funds would only be disbursed if certain conditions were met. That mechanism was promptly referred to the ECJ by Poland and Hungary. It is expected to rule next month.

In the meantime, the European Commission has yet to approve Poland’s share of the RRF. If the ECJ rules that the conditionality mechanism is valid then that could force a rethink by the Polish government, but until then it’s understood that the Polish Covid recovery plan, which each capital must submit, is seen as well thought out in purely economic terms.

That means a question mark remains over the politics and legality of a punitive halt to EU money. The European Parliament, meantime, is taking legal action against the Commission for not moving far and fast enough against Poland.

But member states are genuinely concerned over the principle and mechanical implications of Poland’s actions, particularly in the light of a decade of crisis and euroscepticism.

"Until two years or so ago the far right in Europe was all about exit," says one diplomat. "That didn't work, and Brexit wasn't a great advert for it. Now they have changed tack and are saying, 'we won't leave, we’ll stay and reform Europe from within.’"

It is a crude attempt, says the diplomat, to force back the foundational concept of member states voluntarily sharing sovereignty to create a stronger union, and instead to create a pseudo-union where national sovereignty is jealously guarded, and the existing legal order unravels.

Taoiseach Micheál Martin said that Poland 'had gone too far'

Ireland has taken a strong position on Poland, with Taoiseach Micheal Martin saying Warsaw had "gone too far" and that the Constitutional Tribunal’s ruling was a "slap in the face" for European taxpayers.

The Irish Constitution has a provision that says if EU laws are required for membership, then they have primacy over national laws.

But the government is concerned at the EU single market grinding to a halt if one country does not recognise its legal basis.

More pertinently, as a net contributor to the EU budget, officials say Ireland has a greater interest in value for money when structural or cohesion funds are being spent. If a politicised court in Poland does not fully recognise the primacy of the EU, then judicial oversight of the expenditure of that money becomes compromised.

For now, the emphasis is on the carrot of dialogue and the stick of legal action. The EU’s justice commissioner Didier Reynders has proposed a gathering of national, constitutional judges to meet with their Polish counterparts to discuss a way forward.

But there’s a broader concern. That is that eurosceptic forces, especially in France, where even Michel Barnier has - as a presidential candidate - questioned the role of the ECJ when it comes to external migration into the EU, will press those national constitutional courts into taking a more assertive line on the primacy of EU law.

That means that the timorous approach to spelling out where and how primacy applies could face further challenges.

"If the revolution produced by judicial integration was quiet, the counter-revolution is loud and can no longer be wished away as some pro-Europeans would like," wrote Stefan Auer, Pepijn Bergsen and Hans Kundnani in a paper last week for Chatham House.

"The Polish challenge is part of a historic change in how European integration functions - or does not function."