Greenbelt festival has had a tough time of late. A relocation to a new site in Northamptonshire after 15 years in Cheltenham saw falling ticket sales and some disgruntled punters taking a while to adjust to the changes in culture and experience that a new location inevitably brings. In a world where other Christian festivals have radically scaled back or even cancelled some events because of funding problems, it's unsurprising that Greenbelt, occupying the market niche of a progressive faith and justice space rather than a more traditional (and lucrative) teaching and worship event, suffered last year.

Money was lost. Staff were let go. Trustees wrote publicly about the serious questions Greenbelt was asking itself. The decision was made to shrink the festival in order to make it more viable.

As it experiences the pain and discomfort of change, Greenbelt may also be experiencing the birth pains of a new movement. Greenbelt could be the mother and the milieu of the next Reformation. Right now, Britain's most consistently lovely festival is ripe for massive existential change.

In more prosaic terms, of course, the experience for festival-goers this year will be much the same as the last few festivals. Tickets have been capped at 6,500 and the venues have been cut by a quarter, but anyone who has been to Greenbelt in recent years will know that "not a bewilderingly large enough selection of venues" is a complaint made exactly zero times. According to Mary Corfield, Greenbelt's festival manager, there will still be: "a really good number of people to create great atmosphere and spaces to be in, but you've got a slightly smaller number of people in the campsite and shorter queues at your food vans". Fantastic.

The changes at Greenbelt seem to be good news all round, really: smaller numbers meaning shorter queues and more chance of getting in to see the items you want to, as well as a more sustainable and certain future for Greenbelt as it adopts a capped pre-sale model that makes financial planning easier.

For those worried about practical details and issues that have been raised on discussion boards and in Facebook groups, Greenbelt wants to set your mind at rest. There will be a main stage – it's just going to be inside a tent, and the tent will be big and will have open sides to accommodate super-popular acts. The arriving/parking/getting-on-site/scene-from-Exodus rigmarole will be streamlined, with e-ticketing and a re-planned site with new traffic-flows. The festival will address the peculiarly middle class criticism that it is "too middle class" with continued sponsorship of tickets through the Open Festival programme. There will be worship – though quite a lot of it seems likely to take place among the trees and involve activities like rambles and building dens, for some reason. And everything will stop for Communion on Sunday morning.

Even the vendors Greenbelters love are likely to be the same. "It's not just about the programming," Mary Corfield says. "The experience is bigger than that. It's the caterers, it's the traders, it's the fact that I always buy my grandchild a candle-powered steamboat – those types of things." Corfield says she was pleasantly surprised that traders like the Tiny Tea Tent and other Greenbelt favourites were happy to make the move to the new site with Greenbelt. "En masse, their response was: 'No, we love Greenbelt, we're not going anywhere else.' Because they love the atmosphere and they love the fact that it is so friendly. When they come to Greenbelt they get blessed by it."

Which all highlights nicely that a festival like Greenbelt is so much more than just the programme – and that Greenbelt is, at the moment, one of the most broadly welcoming spaces in the UK Christian calendar. But the worship question in particular is emblematic of the change Greenbelt might be incubating.

Greenbelt Creative Director Paul Northup is clear that Greenbelt is not your classic 'teaching and worship' festival. "There is teaching and there is worship at our event and events that do that are valuable and necessary spaces," he says. "But that's not the space we create." Really, all that's missing from this year's programme is popular contemporary worship. But some online rumblings about a 'lack' of worship at the 2015 festival (while partly due, according to Northup, to punters simply not waiting for the full list of contributors to be announced before drawing conclusions) reflects concerns among some sections of the Greenbelt audience about the spiritual future of the festival.

Greenbelt's great strength, over the last decade at least, has been that it has provided a space where brave conservatives and liberals could go to the same festival without feeling alienated or end up screaming at each other. That this pluralism took place against a progressive backdrop was inevitable, as it has been the progressives in the Church who have characteristically been willing to provide what Northup calls "a generous space – a space that is genuinely inclusive". Greenbelt is an unashamedly progressive festival, but it has always made the effort to include as broad a swathe of Christianity as would be interested in being there. "Whether you come as deeply evangelical, or you come as fringe nonconformist, high Orthodox or Catholic, my hope, aim and intention is to create a space wherein people from all forms of churchmanship and from none can feel welcome," says Northup.

Certainly 'post-evangelicalism' has been a strong force within Greenbelt for many years. But Northup does not believe it defines the festival. "If Greenbelt is post-evangelical, I would say it's also post-liberal," he says. "We wouldn't see that dichotomy between liberal and evangelical as helpful at all." Which is a wonderfully post-evangelical way of looking at it.

Northup says that, like evangelicalism, "liberalism takes us only so far, but not far enough. There's no coherence. There's no community commitment to certain absolutes in how we can make a difference in the world," and that as such, liberalism is unsatisfying. He also stresses, quite rightly, that Greenbelt is not like other major Christian events that tell you where to go and what to listen to. In what some might see as a delightfully liberal way, its very variety refuses to allow the festival to become programmatic. For Northup, Greenbelt has no 'liberal agenda' that some evangelicals might fear.

But the fact remains that last year's festival was the kind of space where the only way a mainstream worship leader was likely to get a standing ovation was if she'd just come out of the closet. In the context of a Church that has for millennia participated in the oppression of gay people (not to mention the ubiquity of the style of music that that worship leader creates), that's a wonderful thing. For those who want it to still be okay to have a different, non-progressive opinion on homosexuality and be at the festival, it may, rightly or wrongly, be a worry. Will a traditionalist on such matters (who nevertheless loves her gay neighbours and isn't going to be impolite at the festival), still be welcome at Greenbelt 2020?

That's the kind of concern that's prompted some to ask if Greenbelt needs to rediscover its spiritual confidence as a Christian festival, to limit the influence of woolly progressivism and post-evangelical Christianity and regain some of its earlier evangelical charact or, at very least, balance.

Northup certainly knows that Greenbelt's value over recent years, as it has hosted Brian McLaren, Richard Rohr and others, has partly been as a crèche-course in progressive Christianity. "One of the gifts that Greenbelt has to offer the Church is precisely to people who have grown up in evangelical settings – to come and experience something which pokes and provokes that a little bit – not in a destructive way, but in a way that is a little bit of grit in the oyster," he says.

But the rise of identity politics (as opposed to pluralist equality politics) among progressives has meant that in order to be perceived as a good progressive, an adherence to easy-going 'I disagree with you but we can happily coexist' liberalism has become insufficient. Recognition, celebration and affirmation of various identities has become the new hallmark of the progressive, and new shibboleths around racial, feminist, LGBT and other progressive causes have emerged. In this context, respectfully disagreeing about a key cause makes someone 'part of the problem' that so many of the good people at Greenbelt are fighting against. And if that becomes the dominant culture among the majority of Greenbelt's attenders (as it is likely to) even the most tolerant and loving traditionalists are going to start finding themselves excluded and alienated by the rhetoric of those who who find themselves on Greenbelt stages quite understandably (and often heroically) fighting not just for equality but for respect. 

Sure, Greenbelt could fight that trend and reaffirm its liberal (in the sense of being a pluralist space for differing opinions) character. It could try to go back to one of its many previous incarnations and reaffirm its identity as a space where conservatives and liberals can learn, worship and debate together. I'd personally love that. I have loved the radical inclusion of Greenbelt as I have worked out my own faith identity. But it may be too late, and that may be no bad thing for Greenbelt.

Because, while Greenbelt is still that kind of tolerant, liberal, pluralist (in the best way) festival, it is incubating something less inclusive within it. Something beyond just the indiscriminate embrace of all identity politics that has swamped the Left. Something more than theological liberalism. An identity and theology and praxis that seems to grow clearer and firmer every month as progressive, liberal, post-evangelical, tolerant and open-minded Christians across the internet and across the world talk to each other, publish and read books and, when they can, go to large events where they can gather in significant numbers. Events like Greenbelt.

If there is a new Reformation brewing, or at least the birth of a movement like evangelicalism, it seems at least conceivable that it would find a nexus in the UK and in a space like Greenbelt, however much Greenbelt itself might not have engineered things that way.

"There has been a sense during its long history that Greenbelt has not wanted to nail its colours to the mast and not wanted to intentionally adopt any position or any responsibility for being at the vanguard, or even part of, a movement or reformation of any sort," Paul Northup says. For him, Greenbelt has always resisted the potential pastoral responsibility for people he meets every year at the festival who call it their 'church'. "That's so deeply theologically problematic that I can't bear it," he says.

Which, in its impulse not to create dependency, and to avoid the traps of hierarchy, establishment and power is very Greenbelt. Even so, Northup recognises something is stirring. "Sooner or later I think that this is one of the things Greenbelt needs to wrestle with and possibly name and talk about more," he says. "[Greenbelt's] role as a sort of church community, a dispersed church community, and what that looks like as part of a global coalition."

Such a 'global coalition', with the likes of Brian McLaren, Fuzz Kitto and other architects and influencers of a new, confident, distinctive form of progressive Christianity, would be a ramping up of what has until now been a predictably loose and free set of affiliations. It's also a bit of a leap to suggest that one can go from preaching, performance and portaloos to papacy or patriarchate. "Greenbelt is just a festival," Northup reminds us. But there's every chance something new may well come out of Greenbelt. And it is unlikely to look like the Christendom it breaks away from.

"I am increasingly persuaded that we ought to be braver about saying that the Church in its established form is dying, in a variety of different ways." Northup says. "Not across all denominations, but certainly in its historic established form it's dying and it hasn't got many years left."

If he's right – and he would not be alone in that view even outside of Greenbelt – just making a space for people who disagree to come together and experience parallel festivals of differing content (as has long been possible at Greenbelt) is probably not going to do the trick.

"I wonder if there is a need for a progressive, joined-up network of people, events and communities to start to more intentionally communicate with each other and co-operate with each other," he says, "so that we can more consciously provide a space to nurture and inspire people who are, for a whole variety of reasons, increasingly feeling disenfranchised or not engaged by more established patterns of Church."

That sounds a whole lot more like a Reformation, or at least a coherent movement, than "just a festival". "It's nothing that's written into strategy, it's nothing that's deeply intentional," Northup qualifies. "But it's definitely something that's been nagging away at us over the last few years."

What with Greenbelt's recent troubles, it's understandable that Northup and others have not been dealing with this possibility head-on. Just as you don't contemplate a globe-spanning, billions-strong, history-altering movement when your leader has just been crucified (or megachurches, successful revivals and a force to rival Rome when God's representative on Earth has just given you a month and a half to recant your life's work).

And now that Greenbelt has regrouped, there is an opportunity, if it wants it, to have a key hand in shaping the more defined movement that will probably emerge from global Christian progressivism (and in reaction to the established traditions who cannot bring themselves to go along). A movement that will emerge with or without Greenbelt's help.

"It's definitely something that we're going to have to wrestle with and name and write about," Northup says, "and do something about pretty soon, I think." He's right. And he's also right when he identifies that what makes Greenbelt great currently is "striking that balance between what people are comfortable with and feel safe with, together with those things that are going to irritate, provoke, inspire, gobsmack people".

Northup identifies that approach as serving people's need "to feel that there's enough on the programme that they think: 'I get that, I recognise that, that's a bit like what I know,'" alongside offering more challenging content. But it is something that may have to be sacrificed if Greenbelt is going to take its natural place as an incubator for a coherent movement rather than a loose association of fellow-travellers.

For Christianity 3.0, Post-Protestantism or Mesa Christianity (or whatever the new denomination might call itself) to succeed, to develop a community to which people can truly belong, it will need to define its identity. And such definitions involve exclusion of what does not fit. Northup, along, I suspect, with many in the Greenbelt fold, will hate the idea of excluding people, particularly parts of the Greenbelt family. It's that generosity of spirit and desire to include that makes Greenbelt so wonderful. But if they don't, they will not have a hand or a voice in shaping the movement that is to come. And there are some voices – strong voices – that could pull it in directions that even those who would wish it every success might find troubling.

I for one would prefer the next step in Christianity's evolution to be guided, at least in part, by the good-hearted, well-intentioned, kingdom-minded people who make Greenbelt, regardless of whether, in the end, I want to be part of that movement.

All photos courtesy of Alex Baker Photography (www.alexbakerphotography.com).