In Greece, the parties they nominated to lead the country through the nightmare of austerity evaporated; decades of political capital and the support of every privately-run TV station proved useless against Syriza – a far-left party whose entire administrative history was contained in five box-files in its shabby HQ in Athens.

In Spain, where several million relatively apolitical people took to the streets in 2011 on a one-way journey away from the political establishment, we have now seen city after city fall to the radical left party Podemos and its local allies.

In Scotland, when accidentally handed the chance to secede from a perennially conservative Britain and start afresh, 45 per cent of people voted to do so – in the face of warnings of disaster from the media, banks and central bank.

And in the British Labour Party, again almost accidentally, the candidacy of a perennially ineffective lone left-winger looks set to dislodge the grip of the centre-left over one of the world’s oldest social democratic parties.

Blair wonders whether to “go full frontal” and take on the left-wing threat, or to “build bridges to it”. For the global political centre this is the right question – but the wrong time to be asking it.

From the Lehman Brothers crisis through the Arab Spring and the Occupy movement this moment of electoral challenge from the left has been coming. But the political centre assumed – not without evidence – that the institutional defences against a swing to the left were strong.

Overturning the elite

Who could imagine a left-winger seriously contending in the US Democratic presidential primaries? Who could imagine Labour’s ragged and ageing parliamentary left mounting a drinks party in a brewery – let alone a challenge for leadership? Who could imagine the liberal-minded, trendy Catalan nationalist elite being overturned by a woman famous for getting arrested on housing protests?

Well, it turned out, masses of ordinary people could.

With Syriza, whose evolution I’ve had the chance to study up close, it plays out like this. In 2011 so many people took to the streets and rioted that when I told Jeremy Paxman about it, live on air, he responded with disbelief.

But it was real. I’d stumbled through clouds of tear gas to watch very ordinary shopkeepers, kebab stall owners, concert pianists, interior designers – the classic small business layer beloved of the political centre – pick up stones and hurl them at the cops.

It was then, reportedly, that Alexis Tsipras, looked out of the window of parliament and told his colleagues: “those are our people”. Syriza, which only formed as a unified party to contest the 2012 election, gathered electoral support – by being credible, restrained, rigorously constitutional – and by focusing on the economic grievances that were driving the left, sidelining more traditional obsessions such as Nato or Palestine.

Once in power, Tsipras took Greece into an economic war with the euro zone he had not expected, nor properly prepared for. Having been forced into a humiliating retreat, and with the loss of a third of his party to the left, he is still leading the polls in the run-up to the September 20th election.

If we ask, in retrospect, Blair’s question – how could the Greek equivalent of Labour have “built bridges” to the people who have joined and voted for Syriza – the difficulty becomes clear.

Syriza right now contains many natural social democrats. Disgusted to the point of switch-off by the patronage and corruption surrounding their old party, Pasok, they built their own bridge – by joining Syriza. Just as young British voters look at Blair and think “Iraq”, young progressive Greek voters look at Pasok and think “austerity”.

When centre-left parties do things that seem inimical to the values of their mass base it takes a long time for the scars to heal. That’s the first problem.

Withdrawal of consent

The bigger problem is: there may not be a bridge to build. What unites the new movements of the left is their withdrawal of consent to the economic system known as neoliberalism. They do not want a left-wing version of it: those with long enough memories know that it was Blair and Bill Clinton who tried to provide one, and that it ended with the financial collapse of 2008.

Unsustainable financial bubbles alongside unsustainable fiscal deficits were the means by which the centre-left of the pre-2008 period “delivered” to their mass base: a cheap mortgage and some tax credits were to be compensation for the loss of high-skilled work and stable communities, which would never return.

All over the world, centrist politics is being challenged from the left and right because the neoliberal economic model is broken; and because the interconnected political and business elite took way too long to listen to what those street protests were actually about.

Yet the left insurgency may only be a phase. The most interesting question of all is: what would a non-neoliberal social democracy look like? Until the centre left starts to answer that it will be left, like Blair, pondering the difference between the reality of Davos, Bilderberg and Jackson Hole, and the reality of mass meetings, packed to the gunwales, for Jeremy Corbyn.

Paul Mason is economics editor, Channel 4 News, and author of Postcapitalism: A Guide to Our Future

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