If you’re still unclear about what David Cameron means when he talks about the Big Society, you’re not alone.

A good proportion of the audience in the hall to hear his conference speech seemed to be reserving judgement, and his own Culture Secretary Jeremy Hunt struggled to define exactly what it meant on Newsnight a few hours later.

Perhaps I can help.  Last night, I was at a packed meeting in the imposing Great Hall of Dulwich College.  It was the first public meeting of the Save the Herne Hill Velodrome Campaign, which aims to secure the future of the South London cycle track – the last surviving venue from the 1948 Olympics.  The organisers had hoped that a hundred people might turn up, they stopped counting at 700 and the speeches and presentations had to be relayed to an overspill room by TV.

The Velodrome, first built in 1903, has been under threat for as long as I can remember and its current crisis is complex.  The track itself is in desperate need of repair and rebuilding, a specialist task which will cost around £200k; the listed grandstand and clubhouse buildings are closed, condemned as unsafe; activities at the site are run by a local cycling club entirely through volunteer effort; the freeholders of the land, Dulwich Estate, have been unwilling to offer leases for more than 12 months at a time, but outside investment has proved impossible to obtain without the guarantee of a longer lease.

Unless a solution is found soon, the Velodrome will close, almost certainly for good.

In a few short months, that solution has emerged in the form of a campaign spearheaded by a small group of passionate, concerned citizens. Their effort has united stakeholders, many of whom previously disagreed, but who now speak with one voice: cyclists and cycling clubs, local residents, children and their parents, schools, politicians, sports organisations, funders, businesses and local historical societies.

From a standing start, the campaigners have generated a significant level of support and publicity, with celebrity endorsements from Olympic stars Chris Hoy and Bradley Wiggins, along with Lord Coe and the Mayor of London’s sports advisor Kate Hoey.  They’ve attracted positive coverage in national newspapers, on radio and TV, and their effective use of digital media has brought a worldwide following of 3,500 people on Facebook.  And 700 people to a school hall on a Wednesday night in October.

It looks very likely that they can now put together a credible proposal for how the Velodrome can be run, and a business plan for its finances, which will convince the local authority and freeholders to guarantee its future.

It struck me half way through the meeting that this mixture of campaigning individuals, skilled volunteers, interest groups, private and public finance might have been what David Cameron meant when he said “society is not a spectator sport”.

Big Society in the flesh.  But saving a much-loved and well-used sporting facility in a prosperous part of London may not be typical of the challenges this idea, and the country, face.

The committee of the Velodrome campaign were able – from local residents and track users – to draw on the skills and time of several lawyers, including a QC; professional graphic designers and website experts; experienced publicists, marketeers and press officers and at least one very senior media executive.  No substitute for hard work and passion, but a big help off the line.

How likely is it that – say – an education project for travellers’ children, or a half-way house for drug users would attract the same level of support and enthusiasm if it was threatened with closure?

Clearly, telling your story effectively and powerfully has never been more important. But how much of a safety net will remain after the spending review later this month?  And how big will Big Society really be?