Natalie says: “The Green surge has carried me to… yes, Caroline, it’s carried us to the seat of power. It has shown that the common good is at the heart of the British people’s concerns… yes, Caroline, and that healing the planet environment thing too. OK, Jenny, and the thing about housing which is going to cost us, I’ve got this Jenny, $2.7bn. I mean pounds. 9bn of them. Sorry, I’ve got a cold. Let me just look at my notes, there’s got to be something about costings. Ah, yes, here.

“I’ll read it out. ‘As leader of the Greens, I love trees. So we’ve not wasted any paper on, uh, working out the cost of our promises. We used this ethically-sourced slate and Manuka wax tabula and this organic bamboo stylus, and we’ve already wiped it clean so it could be reused, sorry.’ Incidentally, as an Australian, agricultural scientist and former Guardian editor, I’m also ethically-sourced, haha.

“Now I’m available for one-on-one photos, no interviews. Please, no interviews.”

Natalie Bennett's excruciating media performances aside, the Green party’s manifesto looks rather attractive to a lefty. It’s all for increasing the role of the state, pushing equality, and actually doing something about all those ethical issues the other parties just tut about and ignore. Their policy website is astoundingly comprehensive and has been kept up to date with their policies for several years. For them, the manifesto just meant they had to compress it a lot.

And their policies are ethical, coherent and radical. For example, the Greens do seem to be the only ones addressing the huge climate change issues, which everyone else in the country seems to be hoping will go away. In Democracy 3, there’s a background temperature increase that represents global warming and affects food production and the like. There’s also a user-created mod to edit it out of the game, presumably for the sort of reactionary fluffbrains who thinks that the 97 per cent of scientists who say climate change is real have spent too long in the sun. But we’ll talk about Ukip tomorrow.

(Incidentally, if you do like simulation games like Democracy 3 and want to try one that will utterly bloody terrify you about climate change, you should take a look at Fate of the World. It’s based on climate science and maps how humanity will survive the next 100 years. Or mostly won’t.)

It's also the party that’s the most radical about equality, and its manifesto is unashamedly redistributive. If I’m to succeed playing as the Greens, I have to hope the ordinary worker is enough to keep the mills of the economy grinding, as I reckon the rich are going to leave the country pretty sharpish.

Finally, it's the party that’s most radical on spending plans. It has a commitment to increasing public spending to nearly half the national income. That’s twice the starting budget in Democracy 3, though only a third as much in real life. I’ll aim somewhere between the two.

So, we start with taxation. It’ll take a long time to get our income up near to 50 per cent of GDP to match public spending, but I’m willing to try. We start with a punitive wealth tax, to represent their commitment to taxing the top 1 per cent an extra £25bn a year and raising the top rate of income tax to 60 per cent. Then we increase corporation tax by a huge 10 per cent. I represent a tax on financial transactions by limiting automatic trading, but I can’t find a satisfactory way to represent imposing controls on bank lending. All these measures will eventually combine to really, really piss off the rich. Which I also believe is a Green policy.

(I say eventually, because implementing policies takes a while in Democracy 3. Some of the bigger ones can take a few years to kick in, which is no good if you’re trying to win a second term.)

After annoying the rich, I raise the tax pledges that will piss off the poor and Jim Jarmusch – cigarettes and alcohol. Then we decriminalise cannabis and tax that too! These taxes actually start pushing poverty up fast, which is pretty awful. Turns out the demand of the simulated poor for these things is price-inflexible, presumably due to rampant addiction and misery.

Once we’ve got cash, we can splash it on our environmental commitments. First, we spend 50 per cent extra on recycling, around £4bn. We put a plastic bag tax in there too, as it seems to fit. The Greens are committed to cutting energy demand by a third by 2020 and to providing £4bn for R&D into less energy-intensive industrial processes. I represent this by raising clean energy subsidies sky-high, and subsidising smart meters in every home. Their commitment to less energy-intensive industrial processes is similarly represented by a green electronics initiative. And we double government science funding, as promised.

We’re now a year in, and something unusual is happening. The inevitable global recession isn’t really affecting the UK. It’s happening, no mistake, but our huge surplus seems to be fending it off, somehow, perhaps because capital is rushing to us as a low-credit risk – or the game might just be misreporting it. Whatever, we’re in an astoundingly healthy situation for this part of the cycle.

We spend our second year fulfilling the Greens’ food and farming promises. A ban on antibiotics in meat agriculture hits farmers hard and pushes up food prices, again increasing poverty. The food standards agency tightens regulations while we add massive subsidies to organic food.

The Greens have also pretty much pledged to get rid of the military and sink trident. So I quietly let all the military go, save for ceremonial duties. We also totally loosen border controls, so Natalie’s family can come visit.

That pays for education. We bump up the schools budget a little and abolish tuition fees (here represented by huge student grants to the tune of £8bn a year).

As we go along, random dilemmas show up. That superhero who kept rescuing those under the Lib Dem regime pops up again. We reject a ban on the hijab in schools (in line with Green policy) and enforce the ban on fox hunting. And we curb banker’s bonuses, in line with our policy on CEO pay caps (which we also impose). I have to say, it really makes a difference in this sim having a searchable policy database. I’d say every political party should do it, but that would mean they’d need to be consistent between elections.

Then something totally unexpected happens. Our credit rating is upgraded to AA. This has never happened to me before, especially not in the middle of a global recession. It reflects my frontloading of taxation commitments compared to putting off big spending commitments, that’s let us pay down the national debt frighteningly quickly.

Despite this, only 8 per cent of voters support us, presumably because they’re being taxed to death. We really need to spend some money to promote growth to get the population back on side and not just the ratings agencies. As evidence of this, two ministers are annoyed over our treatment of capitalists and threaten to quit, so I quickly reshuffle the cabinet.

We establish a national network of electric vehicle charging points (or the closest representation thereof). We can’t renationalise the railways like the manifesto says – but I subsidise them so heavily they may as well be. We cancel all road-building at the same time – another Green policy that saves tons of money, but pisses off half the country.

Next we hit inequality and racism. We put up generous funding for an equality and human rights commission. We maximise the racial equality funding that was already in place, and generously boost the disability allowance. And we impose diversity quotas for companies, to fulfil the commitment to get more women into the boardroom. And we follow the core policy of gently phasing out VAT, which falls mainly on the poor – or rather, cancel it in a day.

A dilemma pops up. Should we ban violent video games? The Greens are opposed to all forms of censorship, so this is fine. Whether we should ban Democracy 3 so I don’t have to stay up all night reading manifestos is another thing.

There are tonnes of other Green policies that would make a huge difference, but that the engine just doesn’t support. I can’t do any electoral or political reform – dissolve the House of Lords, say. We don’t have the legislative power to impose 35-hour weeks or to ban zero hours contracts. We’ve probably achieved a million new public sector jobs from various programs – and lost twice that many closing the road-building programme and the military.

I can’t control bank lending, or break up energy companies, or prevent building on flood plains. I never managed to afford the £20-50bn needed for flood defences. There wasn’t a simple way to prevent airport expanson, dirty power plants or fracking or animal experiments, or to lower the voting age, or to allow euthanasia, or crush private education. But I think we made a good fist of it.

I’m talking in the past tense, because I’ve realised we’re pretty doomed. Our credit rating has been downgraded to BBB, but that’s the least of our worries. Our GDP has collapsed – I thought it would recover but it hasn’t. This is due to the twin problems of a brain drain and a corporate exodus. We have 100 per cent unemployment, which is making GDP drag along the bottom of the graph, so low that the axes markers get in the way of seeing the line. My head honestly just goes down at this point – I genuinely thought this was in the bag there.

We lose, convincingly – though still perform much better than the Tories. I probably could have pulled back a few million votes there at the end, by desperate measures, but it would have been worthless. The Greens were sunk, despite their early victory. Many of their policies inadvertently increased poverty as a small side effect, and it really stacked up, feeding into unemployment, then alcoholism and crime, killing health and productivity.

By contrast, the Greens really did mean to offend the rich, and it worked as I predicted; both rich individuals and corporations fled the country, which destroyed GDP. Despite a huge, ongoing stimulus package, it stopped growth getting off the ground for the last 18 months of the term, which ultimately killed our vote.

It’s a pity, because I was won over by the ease with which everything was funded when you know who the enemy is and the thoroughness of your vision. Despite everything, the Greens made the country better-educated, more productive, healthier and more equal than ever before – indeed, the game deemed the nation a "Green utopia". And we managed to hit our Kyoto goals, by the way. I think Natalie would be happy with that.