At the weekend John McDonnell made a call for the party to support a shift to proportional representation. The case is now overwhelming. But can Labour make the leap to pluralism?

If it doesn’t the spiral of decline will continue. Today only wishful thinking sustains Labour; that somehow, someday it will be returned on its own triumphantly to office and be the people’s champions once more. But the stark reality is that even if Labour can fall over the line first under first past the past (FPTP) it will deliver office and not power – the ability to really transform our society.

The days of a meaningful mandate under FPTP have gone. Even a new New Labour project is impossible to assemble against the backdrop of an economic system that’s isn’t working for a growing majority. The vast bulk of the party has decided irrevocably to turn away from the politics of compromise beyond purpose. But a single Big Tent of the left is equally impossible. The social, cultural, regional and nation tensions are too great for one party to hope for a monopoly of the progressive vote.

A multi-party politics can’t fit into a two party system. The Tories are finding out the weakness of being in office based on only 20 per cent of all voters backing you. And Labour will need to make dramatic changes in terms of greater equality. That demands active and sustained support of a progressive consensus. A good society cannot be built on an undemocratic and out of date electoral system. The old levers of power have rusted up. In a complex society, a progressive future will negotiated with others, not imposed by one party.

So why support FPTP when Labour can’t win on its own with real purpose and can’t govern effectively without deep and broad support? It’s time for Labour to give up on the go-it-alone tribal myth.

By backing PR the party will be in touch with modernity and the way change happens in a networked society. And it will boost the party’s chances of getting the Tories out. A commitment on PR would cement a progressive alliance in which only the Lib Dems can defeat the Tories in the South West and lays the basis for a deal with the Greens. PR would also boost Labour representation in Scotland. This is probably the only hope of defeating the Tories and through it win mandate for electoral system change. This was always Mrs Thatcher’s biggest fear that Labour would cotton on to the way FPTP embeds a Conservative Britain.

But to make the shift it has to be done soon, not as a basis for a last minute and desperate stitch up. Labour should adopt PR because it’s morally the right thing to do – to count everyone’s vote equally. And the issue of a constituency connection is easy to deal with via a system like the Alternative Member System.

The final reason for the shift to PR is the break up of the party itself. There is not point pretending. The now evident different Labour Parties need to go their own away. There has always been more than one Labour Party. It was always a coalition. Only in the past it was held together by the prospects of gaining an overall majority on the misty road to socialism. But something seismic has changed.

The historic failure of revisionism and the break-up of the class base that sustained it has now irrevocably rebalanced the forces within the party. The left was always there but marginal to the project and easily contained. Because social consensus is impossible with neo-liberals the left have eventually been strengthened in the party and the unions, while the right still hold the PLP and the media. Equally matched, they look at each other aghast – how could you possibly not want to win/be principled? The different Labour Party’s can no longer be contained under one roof. They must go their own way. PR allows that to happen without recreating the failure of the SDP. Then they can negotiate honesty in public for different versions of centre and left politics.

More and more Labour MPs are now backing PR. A new All Party Group is to be formed. Meanwhile, and hardly noticed, the TUC has all but shifted its position to PR for the obvious reason the unions cant see the party winning outright again. Tribal yes, but always pragmatic, the unions know some voice is better than no voice. A constitutional convention backed by all parties bar the Tories will help create support for the shift.

The AV referendum in 2011 was the wrong system, at the wrong time pushed by the wrong people. The page has turned decisively. Everyone knows our democracy is broken – no one feels represented except the bankers and the oligarchs. A creeping and persuasive sense of insecurity seeps into the pours of everyone else. Neither capitalism nor Labour is working. Something has to change – it’s called democracy. The time for PR has come. It just happens to now be in Labour’s interests to back it.