London (AFP) - Bitter internal strife, plunging support among voters and surging populism: has there ever been a worse time to be a centre-left party in Europe?

A dozen years ago, left-of-centre giants seemed a natural source of government in many European states.

But today the tally of parties that are declining, sidelined or ideologically adrift is long.

The sick list is headed by Britain's Labour Party, where veteran radical Jeremy Corbyn last week easily won a leadership challenge by centrist MPs angry at his part in the shock Brexit vote.

But political analysts say the venerable party -- founded in 1900 -- faces electoral oblivion despite his victory.

Its dismal standing in the opinion polls is mirrored across Europe.

As with Labour, Spain's Socialist Party is in the grip of a fratricidal war over the performance of its leader, Pedro Sanchez, at a time of national crisis.

In Germany, the Social Democratic Party has lost half its members since 1998.

In France, President Francois Hollande is the most unpopular president in his country's modern history and would be routed if he stands in next year's presidential elections, according to opinion polls.

Centre-left parties recently lost power in Denmark, a stronghold of social democracy, and registered their worst-ever results in Finland and Poland. In Greece, support for the once dominant Pasok has plunged to just six percent.

"Social democracy is a shadow of itself," German political analyst Albrecht von Lucke said on NDR television channel. "We are dealing with decline of historic proportions."

For many commentators, the finger of blame points at globalisation.

They say immigration has become a lightning rod for anger, with older manual workers blaming an influx of foreign labour for job insecurity and lower wages.

"The metropolitan elite think 'great, free movement, we're all multicultural,' but the working class don't really see the benefits and feel threatened by it," says Isabelle Hertner, a lecturer at King's College London.

Story continues

"The average person doesn't necessarily benefit, just the best qualified people. It's difficult for centre-left parties to bridge that gap."

- Far-left insurgency -

Other perceived factors in the centre-left's decline are the 2008 financial crisis, China's entry into the world economy, shrunken public coffers and technological innovation.

Put together, these have savaged the credibility of the "third-way" politics championed by Bill Clinton, Tony Blair and other Social Democrats once ruling Europe.

The model embraced capitalism, globalisation and vast public spending programmes to vacuum up votes among both the comfortable middle classes and industrial heartlands during the booming 1990s and early 2000s.

Post-crash, the traditional far-left became emboldened by the apparent failure of the centre-left's vision of capitalism, and with its subsequent austerity programmes.

"A lot of centre-left parties were actually in power, so you think 'you have not regulated financial markets, so what's the point in voting for you?'" said Hertner.

Anti-establishment feeling and the organisational opportunities afforded by social media helped more radical, tech-savvy leftists take over Britain's Labour Party and fuelled the boom of populist leftist parties across Europe.

"Right across Europe, you've had a trend for new parties to set up with an activist base," said Patrick Dunleavy of the London School of Economics (LSE), citing Podemos in Spain, Italy's Five-Star movement and Syriza in Greece.

"There's been a tendency for parties that were much more digitally organised, and much more aiming at recruiting a mass membership."

- Populism's 'silver bullet' -

Britain's Brexit referendum revealed that many voters in Labour's working-class heartlands turned to rightwing populism, blaming foreign competition and immigration for hastening their demise.

"Populists claim that complex problems can be solved by simple, invariably divisive, solutions," Nick Clegg, the former leader of Britain's centre-left Liberal Democrats wrote in a newly-published autobiography.

"Pull out of the EU. Pull apart the UK. Reduce immigration. Blame Islam. Arrest bankers. Stop free trade. Populism offers silver-bullet solutions to our problems."

With the rights that social democrats fought hard to secure now entrenched in western Europe, these parties are also finding it difficult to convince voters of their reason for existing, said Hertner.

The future is bleak, former Spanish Socialist Party boss Felipe Gonzalez told Spanish magazine Jot Down in July.

"There is no alternative to ending the crisis... and the politics of 'austericide' other than a social democrat manifesto," he said.

"The paradox is that social democracy isn't currently fit to offer this."