Donald Tusk returned to Polish politics on Saturday, in a bid to revive the fortunes of the struggling opposition and dethrone the ruling conservative-nationalist Law and Justice party.

Poland is due to hold parliamentary elections by 2023 at the latest and Tusk, who stepped down as Polish prime minister in 2014 to become president of the European Council, said that he was returning to lead Civic Platform, the centre-right party he co-founded two decades ago, to victory.

“I have come back 100 per cent,” Tusk told a party gathering on Saturday. “My belief [is] that Civic Platform is necessary, not as a flashback, but as a force to defeat Law and Justice in the battle for the future.”

Under Tusk’s leadership Civic Platform became the dominant force in Polish politics, winning elections in 2007 and 2011, the first time since the collapse of communism that a sitting government had won re-election.

But its fortunes were waning by the time he swapped Warsaw for Brussels in 2014, with the party undermined by a scandal over secret recordings of comments by some of its top figures, and accused of having lost sight of the concerns of less well-off Poles.

In the intervening years, Law and Justice, led by Tusk’s arch-rival Jaroslaw Kaczynski, has won a string of local, national and European elections, thanks in part to generous welfare policies, including its flagship child benefit programme, a higher minimum wage, and more money for pensioners.

But it has also set Warsaw on a collision course with Brussels, pushing through judicial changes that the European Commission regards as a fundamental threat to the rule of law, putting pressure on independent media and resorting to attacks on the LGBT movement to fire up its voters.

In recent months, Law and Justice, which rules in coalition with two smaller groups, has been riven by infighting between its moderate and hardline wings. Last week, three MPs left to form their own grouping, depriving the coalition of its formal parliamentary majority, although analysts say it may still be able to cobble together majorities on key votes.

In his speech at Civic Platform’s meeting — during which he replaced Borys Budka as acting head of the party — Tusk took aim at Law and Justice’s record, accusing it of being evil, and of furthering Russian president Vladimir Putin’s goal of dividing Europe through its clashes with Brussels.

“The evil that Law and Justice is doing is so evident, is so shameless, is so permanent, it happens in almost every matter,” he said. “Contempt for minorities, brutal, vulgar authoritarian tendencies, aversion to all types of freedom . . . Permanent attacks on the EU. That’s Putin’s agenda, one-to-one.”

Yet despite Law and Justice’s clashes with Brussels, and tension in the ruling camp, Tusk faces an uphill task to revive Civic Platform’s fortunes. Support for the party has slipped to as little as 16 per cent in recent polls, leaving it trailing both Law and Justice, and Poland 2050, the new centrist party of Szymon Holownia.

There is also a generational split in Civic Platform. Rafal Trzaskowski, the popular mayor of Warsaw, who ran as Civic Platform’s candidate in last year’s presidential election, made clear earlier this week that he was prepared to run against Tusk for the leadership of the party, were it to hold internal elections.

“I think that Tusk will be able to bring Civic Platform back to 20-plus per cent in the polls, and I think that will happen quickly, which will give him something to build on,” said Wojciech Szacki, a political expert at Polityka Insight, a Warsaw-based think-tank.

“But I don’t think it will be enough to overtake Law and Justice in the polls. I think there is a ceiling above Tusk’s head. Poland has changed since he left. Lots of people either dislike what Civic Platform did when it was in power, and others don’t remember it.”