Six years after the crash, the centre cannot hold. Crisis and austerity are delivering polarisation and political fragmentation, and it’s happening almost everywhere across Europe. In Britain the main parties’ share of the vote is shrinking, while Ukip’s rightwing populists are dragging the Tories towards them. At the same time, the Scottish National Party has mushroomed out of the independence referendum campaign as a self-proclaimed party of the left, commanding a level of support that threatens Labour’s chances at next year’s general election. And the radical Greens have overtaken the Liberal Democrats in the latest polls.

It’s a pattern reflected throughout the continent. In the wake of the 2008 meltdown, incumbents were ejected from office one after the other, regardless of political colour. As cuts in services and living standards were imposed in a fruitless attempt to escape the crisis, support for establishment parties plummeted or fractured to left and right.

The main radicalisation has been to the populist right. In mainland Europe, that process began well before the crash, as working-class living standards stagnated under the impact of neoliberal globalisation and the far-right preyed on anti-migrant insecurities. But it has accelerated sharply under austerity. In Hungary the violently anti-Roma and antisemitic Jobbik party took 20% of the vote in this year’s parliamentary elections, while the Front National and Ukip won the European elections in France and Britain.

But radicalisation has been far from one-way traffic. This week Spain’s new leftwing Podemos party, which was only founded in January, overtook the two main parties (and the more traditional United Left) to become the country’s electoral frontrunner, with 27% support. In Greece the radical left Syriza is in the lead with similar polling, five points ahead of the governing New Democracy party. And in Ireland anti-austerity Sinn Féin this week topped polls in the Irish republic for the first time with 26%, following a string of mass protests against water charges.

All three parties are very different, of course. Syriza has its origins in the communist left and has been riding high for several years. Podemos erupted out of anti-austerity and privatisation protests, is strongly critical of the trade unions, and shares some of the “anti-politics” of movements such as Beppe Grillo’s in Italy. Sinn Féin is a working-class nationalist organisation that emerged from a generation of conflict to become in effect a national party of the left.

But they also have essential elements in common – which illuminate what the economic crisis is doing to politics. First, they are all operating in European countries most pulverised by austerity, and drastic cuts in output, living standards and services. Second, they largely come from outside the traditional left and labour movement – and are reacting to economic policies imposed from outside the country by the “troika” of the European commission, IMF and European Central Bank.

And crucially, they are all filling the political gap left by the social democratic and left-of-centre parties that support or are implementing austerity. While parties of the centre-right forcing through austerity are haemorrhaging votes to outfits such as Ukip, social democratic parties are punished even more severely and face potential wipeout.

The flight from European social democracy – after years implementing neoliberal policies that hit core voters – predates the crash. But the embrace of austerity has since taken a far heavier toll, as the internal upheavals and collapse in support for François Hollande’s Socialist government in France have demonstrated. Even in the less baleful economic conditions of Germany, Angela Merkel’s grand coalition with the Social Democrats is leaking support to both left and right — including to the benefit of the Left party, which is about to deliver the country’s first socialist regional premier since reunification.

All of which puts the SNP’s almost 20-point lead over Labour in Scotland in context. The SNP is riding a national tide and isn’t as social democratic as it likes to make out. But there’s no doubt that the demand for social justice and a break with London-imposed Tory austerity were central to the yes campaign for independence. And as Labour’s plans to press on with austerity-lite have become clearer, the way has opened for the new leader, Nicola Sturgeon, to declare that the SNP, not Labour, is Scotland’s real party of the left.

The answer for Labour, you might think, is obvious: break with the New Labour timidity that created the space for the SNP, put the interests of working-class voters who backed independence centre stage, and embrace the progressive mood in the country. One of the candidates standing to lead Labour in Scotland, the Edinburgh parliamentarian Neil Findlay, wants to do just that – and put “clear red water” between Labour and the SNP. But the establishment and media favourite Jim Murphy – the austerity and Iraq war enthusiast who championed campaigning for a no vote in harness with the Tories – wants a return to tried-and-failed Blairite formulas.

That would seal Labour’s fate in Scotland – and possibly the rest of Britain, for that matter. Ed Miliband won Labour’s leadership making clear he understood the failure of the economic model and public revulsion at the elites. When he’s turned that into popular policy, as he did last autumn by promising to crack down on the energy cartels, Labour support has surged. But when Labour’s leaders cling to Treasury orthodoxy and drift back towards New Labour tinkering, the numbers slide and Miliband’s media-inflated quirks take centre stage. The lesson from across Europe is there are no political prizes for embracing austerity – it spells failure in opposition and disintegration in government.