Poland could accidentally leave EU, Tusk warns

"It doesn't matter to me whether Jaroslaw Kaczynski plans to leave the EU, or just initiates some processes which lead to that outcome," Tusk said, referring to the powerful chairman of Poland's ruling Law and Justice (PiS) party.

Tusk compared the situation to the way former British prime minister David Cameron accidentally caused Brexit by calling a referendum for the sake of party politics.

"Cameron also had no plan to take the UK out of the EU. He came up with the idea of a referendum and then did everything to keep Britain in the EU, but [in the end] he led [the UK] out," Tusk said.

"I fear that, in Europe, the will to keep Poland in the EU by all means might be smaller than [was] in the case of the UK," he added.

Tusk's warning on accidental "processes" came after PiS meddling in the judiciary prompted a European Commission sanctions procedure against Poland last year.

It also came after a PiS minister, last month, asked the Polish Constitutional Tribunal whether EU courts had primacy over national ones, questioning a core pillar of EU membership.

But for his part, Kaczynski has dismissed alarmism on 'Polexit' as an opposition "propaganda" stunt designed to discredit his party.

"We've always been pro-European, in the sense of supporting Polish EU membership," the PiS chief said last month.

Amber Gold

Tusk, earlier on Monday, had batted questions on an old business fiasco - the collapse, on his watch as PM, of a firm called Amber Gold, which wiped out €200m of Polish savers' deposits.

The seven-hour grilling saw PiS MPs on a special committee in Warsaw allege that he knew the pyramid scheme was going to fail and did not act.

They accused his son, who had worked for Amber Gold, of dishonesty and, at one point, switched off Tusk's mike in mid-sentence in what was a prickly mood.

The interrogation came after previous PiS subpoenas for Tusk to answer questions on his alleged collusion with Russia on the 2010 Smolensk air disaster.

But the EU Council chief hit back on Monday, accusing his opponents of a smear campaign.

Political intention

"There's a certain political intention, to keep repeating this thesis [of his Amber Gold guilt] ad infinitum," Tusk told Malgorzata Wassermann, a PiS MP who chaired the Amber Gold inquest.

"The committee of inquiry is not a place for conducting the presidential election campaign," Tusk said.

He spoke ahead of Polish parliamentary elections next year and presidential ones in 2020, amid speculation that he might return from Brussels to challenge Kaczynski at home.

He also spoke after local elections last weekend saw PiS gain in rural regions, but lose support in cities, including Krakow - Wassermann's own constituency, which she lost.

"I understand your bad mood, but it shouldn't influence the conduct of this hearing," Tusk needled the PiS inquisitor.

The local election results were a "big warning" that Kaczynski's brand of nationalist-populism was losing traction, he said.