I was midway through a day out with Natalie Bennett, the leader of the Green party, which started with a photoshoot, proceeded to a meeting with the National Farmer's Union in Kent, went round stalls of soft-fruit growers, through some incredibly long conversations with strawberry breeders (that is unfair; the politics of strawberry breeding is like Renaissance Florence) and back on the train to Victoria (she lives in central London), when, in between the pesticide and a surreal conversation with the provider of mass refrigeration solutions (more on this in a minute), she told me the message that she thinks hasn't got across to the uninitiated: that the Green party have more policies than just the ones pertaining to energy. "Making the minimum wage a living wage; renationalising the railways; keeping our NHS public. People, if they listened to me, would quickly realise that we are a complete political party with a complete suite of policies. And they'd see that we're occupying what for many British people is clearly the common-sense place in politics. Something like 75% of people think we should bring the railways back in to public ownership. We have a real problem with our political class, and indeed our media discourse, in that somehow that's still regarded as a radical policy. Even though we all know that privatisation and outsourcing of government services have been an unmitigated disaster – all I've got to say is G4S, Atos, A4e – somehow, challenging the idea that outsourcing is a public good is still regarded as a radical thing to say."

Here I always get a "how do you solve a problem like Maria?" moment – it is plain that the Greens are asking the questions that ought to be asked, that they are organising themselves around precepts that aren't extreme views, but rather, points of fact. There are few serious politicians now who would come out as climate change sceptics, and yet to propose public policy as if you were a sceptic – downplaying renewables, upselling gas, behaving as though it's the 1970s all over again – is perfectly normal. Likewise, there are very few politicians who would make dismantling the NHS their selling point, and yet it feels as though they're vying with one another to see who can do the least to protect it.

While much of the fault for these factors lies with the media – which we'll also come to shortly – there is a sense you get with the Greens that they have almost been neutered by their position as a party. They're trying to do normal politics, with normal leaflets and normal hustings and, via these processes, come upon votes in the normal way of politics. But it's possible that in a 21st-century democracy, you don't persuade people one by one, on doorsteps, in meetings. You might be better off hammering the main parties ceaselessly, devoting yourself full-time to showing how foolish, how self-serving, is the direction of the mainstream. Their advantage isn't in numbers, it's in being right. They have to maximise their advantage.

Later in the day, in a Costa Coffee, Bennett told me: "Well, I used to be a rugby union player. I also used to be a football player, or a soccer player, as we would have said in Australia." This was so far from the answer I was expecting that I looked down to see if I'd made a note of what I'd actually asked. Obviously I hadn't. The 47-year-old leader of the Green party, formerly a Guardian journalist (she edited the weekly international version), previously (by some years) a reporter on a local paper in Australia, originally graduated in agricultural science. "I have a strong competitive streak." Oh yes, that was it – I'd asked what she thought of the political process, PMQs, the yah-boo Westminster atmosphere. I was expecting her to say that it was yesterday's politics, that we would never get sustainable, equitable solutions from a load of chimps leaping up and down, point-scoring off each other (in so many words). What she said instead was: "We have to stop treating politics like a football game. That's what I believe philosophically" – but also, "personally I'd rather enjoy it." I'd trash this stupid game, in other words; but first I'd win.

Bennett often confounds expectation; she's much more pragmatic than I imagined, commenting brusquely about pesticides, "organic production, permaculture production, that's the ideal. But there are a whole lot of steps along the way; reducing 16 times spraying to eight times, that's a pretty big improvement." She is nothing like the pious survivalist that is the caricature of environmentalists (a caricature, incidentally, that goes a huge way towards making these issues peripheral, as everybody looks away, depressed). When she goes to the New Forest, she doesn't spend her time making her peace with the apocalypse, she just wishes they had better 3G coverage. "It's unreasonable to expect people to be saints. That's not what human nature is. But also, if you have a saintly company, unless you create some rules, the devil company will come along and drive them out of business. You need some basic standards."

The issues on which she is unwavering are the ones you would expect: the environmental red lines beyond which no party whose main agenda is climate change could compromise. "We are completely anti-fracking, completely anti-nuclear, pro-energy conservation. It's really important to put that up top, because nobody ever does. Huge amounts of the energy we use is not used for any purpose." Actually, among greens, the nuclear stance is still controversial – there are plenty of people who think nuclear is the best way out of fossil fuel dependency, but that's not where the party is. "Traditionally, Green parties have been opposed to nuclear on grounds of safety, and because we have no solution for the waste. But actually I don't need to go to those arguments. Nuclear is immensely expensive. Anyone who tells you it's going to give us energy in a few years' time is clearly talking through their hat."

Critics from environmental quarters complain that the Greens don't campaign effectively; they could choose single issues – as Oxfam chose foodbanks, as certain children's charities have chosen the minimum wage and others have chosen the cost of childcare – and make that their campaign strategy. They could make more noise, in a more co-ordinated way. While that criticism sounds unfair in the weeks after MP and former leader Caroline Lucas was arrested for her part in the Balcombe fracking protest, it's instructive to pause and consider why they aren't as central to our politics as the German Greens are to theirs (never mind the Scandinavians). What we've witnessed is a series of political muggings – as an election looms, the major parties thieve green policies for the time it takes to portray themselves as a credible government that is also interested in the future; then they abandon them. And this, of course, is mainly a criticism of mainstream political cynicism, but you also have to ask, why don't the Greens hold their own territory better?

Bennett doesn't see it like that, or maybe, sensibly, just doesn't dwell on the historic failure of the party to muscle its way on to the Westminster power axis. She sees a broken two-party system that will, by necessity, make room for another way of doing things: "Two-party politics is clearly not working. What's happened is that they're focused more and more and more on those 100,000 voters in marginal seats. And what's left is a huge number of people uncatered for. That is not a stable situation. It's hard to see how it will change, but it's going to change."

Electorally, she is optimistic, even bullish, about her party's progress. In the recent local elections, which were broadly held as a triumph for Ukip and by that token a disaster for everyone else, she sees the bright side. "We got our first county councillors in Cornwall, in Essex, in Surrey. Obviously, we didn't get the numbers that Ukip did. But those seats were won off the back of a lot of hard work, strong local parties that have been working for years. I could question whether the Ukip councillors have that kind of hinterland. There's a lot more sustainability in our position than there is in Ukip's." (Nigel Farage would have a field day with that remark, though – "party of sustainability find themselves the most sustainable"). A central promise for 2015 is: "We would not go into coalition with the Tories." I suppose voters can guess what the other promises will be. In this peculiarly British system, moving towards coalition, still yearning for old certainties, the smaller parties are going to sink or swim by who they'll get into bed with.

Part of Bennett's optimism for the future, electorally, is rooted in quite a chiliastic – realistic, but still frightening – vision for the future generally. "As we were with economics in 2010, we're still there at the moment, thinking that politics will just continue as it was before the crash. I don't think that's true. People know that economics isn't continuing as it was before. The future is not going to be a replay of the past. It might not even look very much like the past."

It was a curious day we spent together – one minute, we'd have a conversation, and she would succinctly say things that are so obvious it's scarcely creditable that they still need to be said: "Ninety-seven per cent of climate scientists agree. You know, of course there are cases where scientists have universally agreed and been proved wrong in the past. But the evidence is overwhelming.

"Insects and plants are not amenable to human ideology. The daffodils aren't coming up 10 days early because they're on one side or another." Or: "One of the big-risk areas is agriculture and food supplies. The price of food is going to treble. We cannot have the price of food treble and have inequality remain as it is. If you look at the use of foodbanks today, we cannot let that get worse."

The next minute, she'd be talking to a carrot farmer from the north-east, or a soft-fruit grower from Kent, and they'd be, in a very polite way, looking at her as if she were a crank. You could practically see their internal speech bubble, thinking: "Yeah, lady, whatever it is you're saying, I'm sure it's going to cost me money." The body language of the refrigeration posse was comically hostile: arms crossed, eyes flicking back and forth to their hospitality sandwiches, as if the main thing to do with hippies was to keep an eye on them. There was a resolute, courteous determination not to listen to her. And it struck me that this is where public life is, generally – just about polite enough to hear out the Greens, but absolutely unwavering on the decision that normal people, practical people, could not afford – whether financially or politically – to listen to them. How on Earth did we get here? How on Earth did we agree to this, that we'd exist under the spoken agreement that we were in dire environmental straits, and yet accept the tacit, backroom pact to do nothing about it?

Naturally, the media has something to do with this. It has always baffled me how much press attention Ukip gets, for their freak wins based on protest and anomie, compared to the Greens who have an actual position based on a reality that none of us will ultimately escape. Bennett agrees: "I do get very frustrated by the BBC. That's one of the worst places, it's worse than Sky, for getting asked really stupid questions … I'm amazed by how much traction the anti-wind argument has got, with such weak arguments. But I think we've probably fallen for the American idea of independent journalism, where you have one side, and you have to go looking for the other side. There comes a point at which that is an absolute nonsense."

I didn't know Bennett at the Guardian, but in the interests of transparency, I should say that she goes out with my fella's cousin, and I know her personally, not well, but a bit, and I like her. I like the way that she's serious all the way to her core; that she doesn't seem to have any human vanity; that she will turn up to a Green party conference in a green jacket, give a speech against a green background and never even notice that she looks like a tiny floating head off Teletubbies. I like her mental and emotional toughness: the fact that she can look at environmental possibilities and political failures that would make the rest of us want to crawl back to bed, but makes her want to come out fighting. I like the fact that she doesn't have to equivocate because she's always saying something she believes; and the way she doesn't showboat, and doesn't play any of it for laughs.

Mostly, I love the optimism. She is always ready with a positive exemplar: an insulation project in Kirklees, a solar-panelled brewery in Lewes, permaculture, energy-saving ideas, some reason to be cheerful – the greatest of which is, just because things look bad, doesn't mean they'll stay bad. "There has been enormous change, just from my mother to me; there was massive change in the possibilities that were available to me and what people expected of me. Change is the normal human condition. We just tend to be quite short-sighted and not recognise that things have changed massively already." I feel that the Greens are already flying; they deserve better air quality, as will we all, soon enough.