The British Beekeepers' Association, the National Pig Association and the Women's Institute might not be the most obvious partners for documentary makers but it is a sign of a growing crossover between the film world and the third sector that all attended this summer's inaugural Good Pitch.

Held during the UK's Britdoc festival in July, the Good Pitch event attracted a wide range of film-makers with social-purpose projects and the charities, non-governmental organisations (NGOs) and foundations that are interested in working with them. These included Amnesty International, Greenpeace, Christian Aid and The Wellcome Trust.

While there has long been some overlap between film and the third sector - the term used to refer to all charities, NGOs and foundations - the rise of the theatrical feature documentary and the commercial success of films such as An Inconvenient Truth have underlined the fact that social purpose does not have to mean niche.

In the US, the relationship between film-makers and the third sector is well established but in the UK the crossover is only just beginning to expand. This is down to several factors, including a tradition of broadcaster financing.

'The US is a lot further along the line in working in this way,' says Katie Bradford, editorial director of the Channel 4 British Documentary Film Foundation.

'And that's because their public service television system was never like ours. It was incredibly rare for documentary makers to get 100% funding from broadcasters so they've always had to look around for other potential sources of funding. And they've got quite good at it.'

But as TV finance for documentaries gets tighter, UK film-makers are being forced to seek new partners. Striking a relationship with an NGO can bring a number of benefits for film-makers, ranging from help with research and securing interviews to logistical support, finance, marketing and outreach.

Black Gold, a 2006 feature documentary about coffee and trade, worked closely with the third sector. Co-producers and co-directors Marc and Nick Francis made the initial investment to fund the first phase of the project through their company Speak-It Films.

Further research and development money was then sourced from Christian Aid in the UK, and NGOs in Norway, where the film's associate producer had connections with the sector. Together with co-production partner Fulcrum TV, production and completion funding was sourced from foundations and organisations including the UK Film Council's Screen South, the Sundance Institute and the Channel 4 British Documentary Film Foundation. On completion, marketing and promotional support came from the UK's Docfactory.

'What the third sector has helped us achieve - and this is key - is that we've been able to get research and development money from them without us having sold any of the rights for the film,' says Marc Francis.

'So we get a longer and more focused period of being able to develop, without worrying about having sold off territories. We can develop the projects, get them into a really good state and then start engaging with the film industry slightly later on down the line with a more solid, structured proposal and treatment.'

Not just funding partners

Francis says he only sources third sector partners for relevant projects. Speak-It is also developing Cashback (working title), a feature doc about the shadow banking system, and has secured research and development money from NGOs including Christian Aid.

However, China-Africa (working title), another feature documentary the Francis brothers are about to shoot, is funded by Arte, the BBC's Storyville and the Sundance Institute, with no third sector involvement.

'What's amazing about NGOs is how they can help,' says producer Thomas Benski of the UK's Pulse Films, who is producing Gael Garcia Bernal's Resist, an ambitious feature documentary and web project exploring global resistance. 'People miss a trick if they just see them purely as a funding partner because the advantages are much wider than that. They offer you a huge amount of knowledge and expertise, resources, a network on the ground, logistical support, experience. They fulfil so many roles.'

For the third sector, documentaries are attractive because of their power: they can be transformational in a way that reports and web pages are not. 'Black Gold functions on so many different levels depending on where you're at as an audience member,' says Deborah Burton, a global campaigner for Christian Aid.

'If you know nothing it tells you a lot. If you already knew about fairtrade it moves you on to the wider trade picture... Film can be an incredibly effective way of shaping the way society thinks about an issue and working as a tool to share with your supporters.'

The chance to work with talented, passionate film-makers is also key, says Amnesty International's creative relationship director, Chloe Baird-Murray. 'There are people out there who are incredibly passionate and skilled, with the most creative minds and ambition and drive, who can make their own film and tell the story that we're trying to tell. And we can work all the way through with them.'

Amnesty is working with a range of projects including Erasing David - about identity and privacy - as well as Bernal's Resist. The charity is also launching an arts fund later this month with a view to funding more creative activism.

In addition to production support and finance (the big US foundations invest up to hundreds of thousands of dollars), third-sector organisations are also sophisticated communicators with sizeable networks of supporters who can become advocates of a project - and boost its release.

'We have very strong groups and networks both in universities and in local communities, who are like an army of volunteers,' says Amnesty's Baird-Murray. 'Those are the people that get things seen on campus, who make sure that their cinema takes a film.'

Knock-on effects

Black Gold's Francis says: 'If the third sector really likes the project you're working on and they start campaigning to their members and saying: 'This is a film that you really should see', that can give you bums on seats, which can really help you at the box office. And it can have wider knock-on effects.'

Like any relationship, choosing the right partner for the right reasons is crucial - both for film-makers and the third sector. 'It's the job of a producer to choose carefully who to engage with,' suggests Pulse Films' Benski. 'That's one of the key challenges when you get involved with NGOs: understanding exactly what that specific organisation is trying to get across, trying to get out of the film... It's about defining the strategy of the project, defining the core values of the project. Not just the film but the project: what do we want to achieve' What is our position' What is it that we intend to do and how will we do that''

Control is a key issue. 'We're coming at it from the perspective of serious film-makers wanting to tell engaging stories,' says Francis. 'That for me is the key thing because in engaging the third sector it's about making sure whatever funding one receives is not in any way going to affect the way we tell the story.'

There is an element of risk for a third-sector partner to get involved with a film that may not turn out to be a precise fit with their campaigning position. 'The issue is establishing that degree of trust so (a third sector partner) knows that whatever comes out at the end is going to be positively helpful to them even if it's not 100% what they would have made themselves,' says Christopher Hird, executive producer of Black Gold and the forthcoming The End Of The Line (see box).

For Christian Aid's Burton, 'It's (about) knowing that as an NGO you are comfortable with what the content thrust of the film is going to be,' she says. 'That you're not going to end up getting involved in a film that goes against what you stand for or are campaigning on. That it resonates for you.'

And films are resonating more and more with the third sector in the UK. 'It's a chicken and egg thing,' says Bradford, who is working on Usefilms, a matchmaking website for film-makers and the third sector that will launch in January. 'The more you can prove the impact that documentaries can have to these partners, the more partners will come on board. It's a process that's happening.'