Jeremy Corbyn has been elected Labour leader with a stonking great majority. He arrives with a vast mandate from a bigger membership than any UK party has had in the modern age. The political year which started with Scotland's independence referendum has ended with an event perhaps just as extraordinary.

I'm a member of the Green Party. And for Greens, this presents a challenge. On the one hand, many members are delighted to see someone they have marched alongside over the years as leader of the opposition. On the other, the party's strategy in recent years has at least in part been to occupy space vacated by Labour. A huge proportion of those who joined the party during the Green Surge did so because they saw the Greens as “the only party left on the left”. Clearly, that's no longer true.

With this in mind, here are some thoughts on how Greens should respond.

1) Embrace the joy

It's easy for Greens to look at Jeremy Corbyn and feel a little like François Englert must feel watching Peter Higgs: “those were our ideas too, how come he's getting all the credit?”. Similarly, it's tempting to sneer: Corbyn might be left, but his ideas represent the past, not the future.

This is the wrong approach. The election of Jeremy Corbyn brings an anti-establishment voice to the front bench and profile to a range of issues Greens have long campaigned on. It's a stab in the eye, foot, knee and cheek for the neoliberal consensus and that's all to the good. It's easy to sit moping in the corner muttering snide remarks about how the music's terrible and everyone's gonna wake up with a hangover, but since when was that a good way to make friends?

In particular, Corbyn will face a brutal assault from the forces of the establishment for as long as he remains leader. Greens shouldn't join in the kicking, but show some solidarity. The Greenwich Greens demonstrated perfectly here.

2) "Yes, and"; not “but, but, but”

Corbyn and the Green Party agree on a huge amount, including perhaps their respective most popular policies: opposing austerity and privatisation. However, Greens have much more to add to this: ideas for the future like basic income, giving workers the right to turn their companies into co-ops, democratising the energy system from the bottom up, participatory budgeting, land reform and land value tax, and so on.

These aren't proposals that Corbyn would necessarily oppose (he's said he's interested in a social wage – which is a similar idea to a basic income). And so the tone shouldn't be moral outrage at the failure of the Labour party to adopt these ideas, but rather, “yes, and”: “yes, it's great that Labour now has a leader who opposes austerity, and let's get serious about abolishing poverty with an unconditional basic income”.

For the last five years, Greens have had to start pretty much every conversation by making a case against austerity. Scottish Green co-convener Maggie Chapman was even asked by the BBC how the government would pay for her proposal that the minimum wage be raised to a living wage: a measure which would in fact bring money into the Exchequer. With Labour now likely to articulate this argument, Greens have cover to explain more radical policies – a position which has helped the party to rally support in Scotland during the referendum. This is an excellent opportunity, one that the party should embrace.

3) The future is about radical democracy

Radical democracy is one of the Green Party's four founding principles, and it's an area on which Corbyn is a little weak. He comes from a relatively economistic tradition which sees progressive politics as about redistributing wealth, but talks less about political power. He's luke-warm on PR, opposes Scottish independence and seems to have little to say about, for example, regional assemblies in England.

Redistributing wealth is vital. But, as Neal Ascherson has said (also quoted by Anthony Barnett this weekend), you can no more get democratic socialism from the British State than you can get milk from a vulture. Britain is a collection of rocks in the North Atlantic run by a system designed to control the biggest empire in human history. Until that changes, little else will.

Corbyn has said, when pushed, that he supports the idea of a constitutional convention from opposition. Greens should enthuse him about that to ensure that it happens, and then collaborate with it as much as possible. Such a convention, properly run, has the capacity to release vast energy in England and to turn a temporary wave into a permanent shift in the democratic structure of this country.

Deep down, people know that British politics isn't fit-for-purpose. The first ever Green Party national campaign, in the 1990s, was “the Campaign for Real Democracy”. Perhaps it's time to launch this again.

4) Prepare for different futures

Politics is clearly changing. Making confident assertions about what will happen next is like using a road map in space. Almost no one predicted that this would happen, and so almost no one can reasonably claim to be sure about what will happen next. Greens should be flexible, solidaristic, joyous, honest and friendly, not snide, bitter or know-it-all. If Corbyn or a similar successor (Lisa Nandy and Clive Lewis are obvious potentials) is the Labour candidate for Prime Minister in 2020, then the party should be prepared to form an electoral pact – as Caroline Lucas has proposed, and which Elliot Folan has looked at in more detail.

One of the big failings, in retrospect, of the Greens this year was not managing to persuade the SNP to agree a Westminster electoral pact. The idea that the Greens would stand down in all but, say, two seats, and the SNP would stand down in those was widely discussed on both sides before the election, but didn't eventually happen.

The Scottish Green vote in two of the three seats the SNP didn't win – Edinburgh South and Dumfriesshire, Clydesdale and Tweeddale – was bigger than the winning margin, whilst Greens failed to make any significant gains. What-ifs are always difficult, it seems likely that such a deal could have delivered an extra Green MP or two, and ensured that neither Labour nor the Tories held any seats in Scotland.

On the other hand, if Corbyn is deposed at some point in the next five years, the Parliamentary Labour Party refuses to nominate anyone similar to run as a successor, and Labour runs in 2020 with a leader from the centre or right of the party, then Greens need to have built a lifeboat capable of carrying the vast hopes of the movement that has emerged out of Labour and into that election.

5) Prepare for next year's election

2016 brings a series of vital elections in Britain: London, Wales, Scotland, Bristol, Liverpool, Sheffield and Northern Ireland if the Assembly manages to limp that far (which is looking less and less likely).

Most of these votes take place in systems other than first past the post: the Mayoralties with a supplementary vote system, and Scotland and Wales with the additional member system. In London, a “Sian then Khan” campaign seems an obvious way forwards. The idea that Liverpool's Labour Mayor Joe Anderson is the progressive candidate in that race will be difficult to sustain, irrespective of what his party leader says. Bristol is a whole different ball game, and that's before we even think about Scotland.

6) Don't retreat from the left

The simple and obvious lesson of Corbyn's victory is that left wing ideas are back. For Greens to retreat into a narrow eco-liberalism now would be an absurdity. The best electoral chances for Greens lie either in mopping up the Corbyn support after a Labour coup or in an electoral pact with a Corbynite candidate for PM.

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