By Hugh Williamson in Berlin

Some of the shine was taken off Oskar Lafontaine’s leadership of the Left party, the powerful new force in German politics, at the weekend when he suffered his first setback at the hands of the party’s activists.

Seeking re-election as chairman, Mr Lafontaine won the backing of only 78.5 per cent of delegates to a party congress, compared with 88 per cent who elected him a year ago. Left officials had predicted at least 90 per cent support for Mr Lafontaine in Saturday’s vote at the party’s first official congress, in Cottbus, eastern Germany.

For many political leaders the result would represent a triumph but for Mr Lafontaine – one of Germany’s best-known politicians – it was a warning.

The group, with about 12 per cent of national support in opinion polls, has this year emerged as Germany’s third most powerful party after the ruling Christian Democrats of Angela Merkel, chancellor, and their coalition ally, the Social Democrats.

Created in June 2007 by a merger of east German ex-communists and disgruntled west German SPD members, the party has already forced Germany’s mainstream parties to shift leftwards on many economic and welfare issues, and to consider new options for coalition-building in national and regional parliaments.

Following recent successes in three regional elections in west Germany the party, with 73,000 members, now has seats in 10 of the 16 regional assemblies, plus the national parliament.

But the weekend vote, combined with other signs of unrest in the party, suggest it now faces greater scrutiny, from both its own followers and the public.

Archives released last week suggest that Gregor Gysi, the Left’s parliamentary leader, may have in the 1970s informed for East Germany’s Stasi secret police. In Cottbus he denied any wrongdoing.

But it is Mr Lafontaine, a former chairman of the SPD, who is really in the spotlight. Critics in the party dislike his overly populist rhetoric, his allegedly authoritarian style and his “westernisation” of a predominantly eastern party.

Katina Schubert, an outspoken rebel within the Left’s leadership, said after the Cottbus vote that it reflected concern over “Mr Lafontaine’s leadership approach”.

That is not how the issue is seen by Mr Lafontaine’s supporters in his home state of Saarland, on Germany’s border with France. Here, the 64-year-old is a hero, credited with making the party electable for disaffected voters, both in this industrial region and in west Germany as a whole.

Winfried Jung, a tram driver and SPD member for 28 years, says “Oskar” has successfully highlighted the alleged rightward drift of his former party. “The SPD no longer stands for ordinary people and for social justice. The Left does – that’s why I joined them,” he says in an interview in the party’s shop-front headquarters in Saarbrücken.

The Left’s pacifist agenda, including withdrawal from Nato and pulling German troops out of Afghanistan, has also struck a radical chord, while Mr Lafontaine’s Robin Hood approach of taxing the rich to help the poor has hit home in a country that, despite its economic upswing, is unsettled by globalisation and welfare cuts.

“The Left offers the only clear alternatives on these issues,” says Barbara Spaniol, a Saarland legislator who recently defected from the Green party.

Yet observers, and the Left’s opponents, doubt how clear these policies are. Among them is Peter Müller, Saarland’s Christian Democrat premier: “The Left party can promise the earth with no sense of responsibility on how such promises could become reality.”