There was a sharp retort from the European Commission president, Jean-Claude Juncker, to Hungary’s Trump-like demand this week that Brussels pay for its controversial border-fence defences against migrants.

His letter landed just as the European Court of Justice also told Hungary that its refusal to accept its quota of migrants relocated from Greece and Italy was illegal. The mandatory quotas had been agreed as a burden-sharing measure by member states to help the two countries facing a tidal wave of refugees in 2015.

Juncker noted that during that crisis Hungary declined “the possibility to benefit from [the] relocation of up to 54,000 persons and decided to return nearly €4 million of EU funds prepaid by the Commission to Hungary”.

“Solidarity is a two-way street,” he said in his letter this week to the Hungarian prime minister, Viktor Orbán. “There are times in which member states may expect to receive support, and times in which they, in turn, should stand ready to contribute.

“And solidarity is not an à la carte dish; one that can be chosen for border management, and rejected when it comes to complying with relocation decisions that have been jointly agreed.”

He pointed out that Hungary receives EU subsidies amounting to more than 3 per cent of its GDP each year, the highest percentage of any EU member country.

The exchange and its tone reflect the tense state of the relationship – compounded by court proceedings – between the commission and Budapest over other issues, like restrictions on the operation of universities and NGOs that receive foreign funding.

Poland’s judicial “reform”

And, very much in the same vein, Reuters reports that the commission will be asking member states at the next general-affairs council, later this month, to back its legal action against Poland over its judicial “reform” programme.

Concerns about the rule of law and democratic rights in both countries and about their “à la carte” approaches to “solidarity” between member states are providing a real challenge to the European Union and, specifically, the idea of “political union”, common understandings and benchmarks of legal and human-rights standards.

What is seen as “slippage” in basic legal standards in Poland and Hungary “threaten the EU more than Brexit does because they undermine the union’s legal foundations”, an article for the the Carnegie Europe think tank argues this week.

Its authors, Heather Grabbe and Stefan Lehne, make an important case that the time has come for member states to take up the baton on these issues from the commission and the European Parliament, whose attempts to rein in Budapest and Warsaw have been treated with little more than contempt. “Hungarian and Polish governments will feel the heat only if political leaders of the EU’s other member states get actively involved,” the piece argues.

Things may be changing. The German chancellor, Angela Merkel, abandoned her usual restraint last week by criticising Poland’s governing Law and Justice, or PiS, party. On Tuesday, one day after the Polish government dismissed the EU inquiry into its judicial changes as groundless, the chancellor said she took the commission’s worries very seriously.

However much I want to have very good relations with Poland . . . we cannot simply hold our tongues and not say anything for the sake of peace and quiet

“This is a serious issue, because the requirements for co-operation within the European Union are the principles of the rule of law,” Merkel said in Berlin. “However much I want to have very good relations with Poland . . . we cannot simply hold our tongues and not say anything for the sake of peace and quiet.”

At stake is not simply a moral or normative argument about the merits of democratic norms, Grabbe and Lehne argue, but the effective functioning of cross-EU legal systems based on mutual trust and respect. German companies complain, for example, that they don’t get a fair hearing in the Hungarian courts and worry the same could happen in Poland.

“Deep integration requires deep trust,” the article argues. “EU members recognise the decisions of each other’s courts and rely on each other’s regulatory institutions to implement product and environmental standards.”

Similarly, the mutual enforcement of arrest warrants is likely to break down if prosecution systems are seen to have become politicised.

Open defiance

And in Hungary and Poland the problem is not just about damage to the rule of law but also about open defiance of legally binding decisions by the European Council or the European Court of Justice.

Part of the problem in getting compliance with EU standards lies in the inevitable reluctance of heads of government to criticise fellow leaders – some day, they reckon, it will come back at them. Not surprisingly, they made treaty provisions for controlling errant member states almost impossible to apply. Article 7 of the current treaty provides for the removal of the voting rights of states in persistent serious breach of EU standards, but it can be applied only by the unanimous vote of the other states.

Hungary and Poland together can block any move against the other.

For now pressure can best be applied through court orders and political pressure from fellow leaders. Germany and other countries are also considering, however, whether to propose new conditions that would tie access to EU funds to a country’s performance on governance and the rule of law, and willingness to implement practical solidarity measures like accepting refugees.