In 1867, the Representation of the People Act saw a massive expansion of the male franchise.

That came about after an unusual parliamentary event: opposition amendments to a Tory government bill were not resisted, but slid through without serious challenge from the front benches. They made the bill vastly more powerful and had effects far beyond what had originally been intended.

This was a cross-party effort that led to a shifting of the tectonic plates beneath British politics. It was driven by the campaigning of the Reform League and massive public support.

The size of the electorate more than doubled, and the (then radical) Liberal Party benefited hugely.

People in the future might well look back to an event this week and see in it the seeds of the same scale of transformation, with a similar approach.

For representatives of all of the political parties, and many campaigning organisations, are signing up to a single document, the Good Systems Agreement, that provides a clear, simple route forward to get ourselves out of the current political mess.

All are agreeing to the rapid move to a fair, proportional, method of electing the House of Commons, and a people’s constitutional convention, or similar citizen-led process, to agree the details of how that should work.

It is being driven by Make Votes Matter, like the Reform League a relatively new organisation that sprung up after previous campaigning groups such as the Chartists had failed to achieve the changes they’d worked hard for.

I’ll be delighted to be there, bringing the Green Party’s long-term support for the democratisation of our politics, the essential modernisation that has been blocked by a century of inertia, with no significant changes to the structures of the House of Commons since women won the right to vote.

Public hunger for change

There’s certainly the same kind of public hunger for change that there was in 1867. Agreement that our politics is broken is pretty much universal.

It is very tempting to blame individuals for the disastrous state of Britain today, the Brexit chaos, the poverty and inequality, the insecurity and mental health crisis, the dreadful state of our natural world and the climate chaos.

And certainly they have to bear a share of the responsibility – the frantic race to the furthest extremes of Brexit that we are seeing from our Tory leadership candidates should provide no excuses.

But it is clear that the failure is systemic. In the last general election, 68 per cent of votes didn’t make a difference towards the outcome. In 2015, the Tories got 100 per cent of the power with less than 37 per cent of the votes cast.

That the people are desperate to 'take back control' of their communities, their lives, their futures, is no surprise at all. Our antique, undemocratic system has shut so many out of politics for so long. The solution can only be to change to a system in which the views of voters are reflected in parliament – a system of Proportional Representation.

Consensus-based politics: Putting differences aside

We know that proportional systems produce better decisions and better policies, with people working together to contribute to the best way forward rather than remain at loggerheads as Parliament has been for so many months.

This makes the new cross-party agreement an elegant way forward, as well as an essential one. It is bringing a modern, consultative, cross-party approach to designing the kind of system that will make those decisions the normal form of politics. It is the kind of decision-making that is normal in most of the rest of Europe – and indeed in the European Union.

The signatories to the Good Systems Agreement have huge political differences. But they know that the people are demanding change and that they can all find agreement on this crucial point. That means they can not only work together, but make a stronger force, because they are representatives of so many different perspectives.

It is clear that the failure is systemic. In the last general election, 68 per cent of votes didn’t make a difference towards the outcome.

There’s a further parallel with 1867.

One of the challenges of dragging the electoral system for Westminster into the modern age has been what’s often described as the 'turkeys voting for Christmas' problem.

MPs elected under the current system, its beneficiaries, are reluctant to change it, to their possible personal detriment.

What they need to see is a clear drive from the people they are supposed to represent, and a clear route that doesn’t allow enthusiasm to be sunk into technical arguments about “which system” or “what size constituency”.

Let’s agree to the need to change, and then use an impeccably democratic process of a people’s assembly to let the people decide the details.

We need to break the political deadlock. Going toe-to-toe through confrontational politics is how we have got where we are today.

Co-operative working, consensus-building, looking around the world for the best practice and putting it in place is what has got us to this historic agreement on electoral reform. It is also what will put it into practice.