European Council President Donald Tusk urged his fellow Poles on Monday to "come to their senses" over Poland's place within the EU, saying it could otherwise end up following Britain's example and tumble out of the bloc.
Tusk, a centrist who served as Polish prime minister from 2007 to 2014, is a strong critic of the ruling eurosceptic Law and Justice party (PiS) in Warsaw, which has often clashed with Brussels over immigration, the rule of law and other issues.
Tusk, who chairs EU summits, said that in 2016 Britain's then-prime minister David Cameron had not intended to take his country out of the bloc when he called a referendum, adding that Poland too could exit as a result of political miscalculations.
"It does not matter to me whether (PiS leader) Jaroslaw Kaczynski plans to leave the EU or just initiates some processes that lead to that outcome," Tusk told reporters during a visit to Warsaw. "The issue is that Cameron also had no plan to take the U.K. out of the EU. And the will (among member states) to keep Poland inside the EU is smaller than the will to keep the U.K. in it."
"This issue is incredibly serious, the risk is deadly serious, I want everybody to come to their senses," Tusk added.
Warsaw has no plans to hold a U.K.-style referendum on remaining in the EU, which it joined in 2004, but the European Commission is conducting an unprecedented investigation into the rule of law in Poland as well as several legal cases.
Last month, ahead of local elections, it turned out that the Polish justice minister asked the constitutional court to check whether EU law was compatible with the Polish constitution, triggering anger among Poland's generally pro-EU voters.
His comments helped independent and liberal candidates to win most mayoral posts in Polish cities and towns, limiting the overall scale of PiS's gains in the local elections.
Tusk said those results served as a "big warning" for PiS.
He declined to say whether he planned to return to domestic politics when his mandate at the European Council expires in late 2019.
Poland faces a parliamentary election next autumn. Poland will also vote along with other EU member states next May for a new European Parliament.
Since sweeping to power in 2015, PiS has remained broadly popular, benefiting from voter-pleasing welfare reforms, nationalist rhetoric and strong economic growth.
But critics at home and abroad have accused it of a tilt towards authoritarian rule after moves to increase government control over the judiciary and state media that have also fueled Poland's isolation within the EU.