Gianni Pittella, leader of the European Parliament's socialist group, has rejected a call for further cooperation with the parliament's centre-right EPP group, in a move that could shake up the power balance of the house.

Pittella dismissed a plea for further cooperation made by EPP leader Manfred Weber in a letter to all MEPs as "quite amazing" and "surrealistic".

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"The European Parliament works perfectly without structured alliances," Pittella said on Tuesday (13 December).

"Conservative Europe is taking us down the wrong road. We need change."

In effect, Pittella had already ended a long-standing pact with the EPP group by announcing his candidacy for parliament president. Under their agreement, the role should have gone to the centre-right bloc.

Worried that this could give a stronger voice to far-right forces in the house, Weber sent a letter to all MEPs on Monday urging pro-European forces to unite.

Weber told reporters on Tuesday: "For the last 2.5 years, we didn't have any legislative decision in this house without a compromise between the EPP and socialists. Either we carry on working on the basis of consensus, or we conduct party political games and everyone will fail."

He said a failure to cooperate could open the door to populists such as France's Marine Le Pen or the UK's Nigel Farage to become "kingmakers".

Campaign trail

It was uncertain, however, whether Pittella's bid for president would win the backing of other progressive groups, such as the liberal Alde and the Greens.

Liberal leader Guy Verhofstadt is mulling his own bid, and will announce this week whether he is running or not.

The Greens hinted they could back an EPP candidate. Green co-chair Philippe Lamberts said the group's stance would become clear once the EPP candidate was elected on Tuesday evening.

The EPP is the only group of the European Parliament to elect its candidate for the presidential post in a primary rather than in-house selection.

Meanwhile, Weber's strong anti-populist rhetoric has angered groups such as the left-wing GUE/NGL, which doesn't want to be put in the same bag as far-right, racist parties.

"Mr Weber seems to forget he has Fidesz in his group," GUE MEP Helmut Scholz told this website, referring to the party of Hungarian prime minister Viktor Orban.