EU lawmakers elected a Spanish Socialist as their new president Tuesday, but the deal was immediately slammed as a "grubby stitch-up" as politics-as-usual resumed in the newly-expanded parliament.

The Strasbourg assembly, meeting for its first full session since the EU's May enlargement, also received a warning from eurosceptics who vowed to "wreck" the parliament after boosting their presence in June elections.

The comments came at the start of a three-day plenary meeting which is also expected to approve the nomination of former Portuguese prime minister Jose Manuel Durao Barroso as head of the European Commission.

Borrell, a former Spanish transport and treasury minister, was elected on the first attempt by the 732-member assembly, the European Union's only directly-elected body.

A total of 388 MEPs backed Borrell to succeed Irish liberal Pat Cox wielding the Strasbourg gavel, against 208 for his main rival, former Polish foreign minister Bronislaw Geremek.

Political leaders confirmed that a deal between conservatives and socialists handed Borrell the presidency, but only on agreement that he hand over to the conservative European People's Party (EPP) chief Hans-Gert Poettering of Germany in 2006 for the rest of the parliament's five-year-term.

While Borrell won ringing tributes from his supporters, Liberal group leader Graham Watson reiterated his opposition to the power-sharing deal between left and right. "The alliance they have formed is an unnatural one," he said.

Scottish National Party MEP Ian Hudghton went further: "Today's stitch-up .. is a grubby and thoroughly unprincipled attempt to secure positions of influence behind closed doors," he said.

The Strasbourg session was the first full meeting of the Parliament since the May 1 enlargement of the bloc from 15 to 25 member states. Previously there were 626 MEPs.

On Wednesday Durao Barroso is due to address the parliament, ahead of a vote Thursday on his nomination to succeed Italy's Romano Prodi as head of the European Commission, the EU's executive arm.

The former Portuguese prime minister emerged last month as the compromise choice, and has the backing of the EPP. He is widely expected to win despite leftists' concern notably over his backing for the US-led war in Iraq.

But as the heavyweights concentrate on power-play over key EU posts, others will have their sights on other causes: putting a spanner in the bloc's institutional works.

Eurosceptic parties made gains across the EU in the June elections: notably in Sweden where the June List won 14.4 percent, in Poland where two anti-EU parties scored nearly 30 percent between them and the Czech Republic where the main opposition Civic Democrats scored nearly 30 percent.

Britain's UK Independence Party, one of the most high-profile eurosceptic groups which boosted its presence fourfold in the Strasbourg assembly in the June ballots, wants Britain out of the EU altogether.

Shortly before Borrell's election UKIP's parliamentary leader, Nigel Farage, ceremonially ripped up his ballot paper in a press conference in the sidelines of the parliament session.

The party's star, former television presenter Robert Kilroy-Silk, reiterated his pledge to "wreck" the parliament by exposing its fraud and corruption.

"We do not wish to rain on their parade, we do not wish to spoil their party," he said. "It is simply that we do not want to belong to their party, because we want to govern ourselves."