Italy’s deputy prime minister, Matteo Salvini, has renewed his pledge to change Europe as his rightwing coalition swept to victory in the southern region of Basilicata, ending 24 years of leftwing rule.

Basilicata is the third region won by the coalition, which includes Salvini’s far-right League, Silvio Berlusconi’s Forza Italia and the smaller far-right party, Brothers of Italy, since the League formed a national government with the Five Star Movement (M5S) last June. The group scored almost 43% of the vote, 18% of which came from League supporters.

“In one year the League has tripled its votes, victory also in Basilicata!” Salvini tweeted. “Goodbye to the left, and now to change Europe.”

Sunday’s vote marked another dismal result in regional elections for the M5S, an outcome that will further test the party’s influence within the national coalition as its partner, the League, flourishes.

Although the M5S was the single biggest party in Basilicata – winning just over 20% of the vote – it lost more than half the support gained in the region in last year’s general elections.

The leftwing coalition came second, with the outgoing Democratic party gaining less than 10% within the group despite hopes of renewed vigour under the recently elected leader, Nicola Zingaretti.

The party’s image was sullied by the house arrest last July of the region’s president, Marcello Pittella, for alleged corruption. The Pittella family had been somewhat of a dynasty within the administration since the mid-90s.

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“Basilicata was maybe tired of the centre-left and after a scandal it was easier for the centre-right to win the election,” said Mattia Diletti, a politics professor at Rome’s Sapienza University.

While the win was crucial for Salvini, it was also a success for Berlusconi, who is plotting a political comeback and is running in May’s European elections; the region’s new president, Vito Bardi, a former financial police governor, is one of his closest allies.

The M5S has been gradually losing consensus since coming to power with the League and the defeat in Basilicata follows losses in Abruzzo and Sardinia in February. The arrest last week of Marcello De Vito, a senior M5S figure and president of Rome’s city council, over alleged corruption, an issue the party has long railed against, has added to its woes.

Since last April, the rightwing coalition has won elections in the regions of Molise, Friuli-Venezia Giulia, Abruzzo and Sardinia, as well as the Trentino-Alto Adige province of Trento. The alliance will also vie in votes this year in Calabria, Emilia-Romagna and Piedmont, all of which are currently under a leftwing administration.

But for now all eyes are on the European parliamentary elections in late May, and in the absence of any real challengers, Salvini is forecast to win big. He has reportedly invited members of the far-right grouping, Europe of Nations and Freedom (ENF), to Rome in April, with the aim of forming an alliance. Salvini has strong relations with National Rally, the French far-right party led by Marine Le Pen.

“You never know with Italy, as sometimes a scandal or event can alter a path, but right now I can’t see anything that will change a Salvini victory in the European elections,” said Diletti.