Pints, camera, action!

And now: CAMRA the Movie! The Campaign for Real Ale is celebrating its 40th anniversary this year and to emphasise the point a film has been launched that traces the history of the movement and its success in saving cask beer.

The History of CAMRA is a remarkable film in many ways. It traces not only a consumer revolt that has saved a unique beer style, but it's also a major documentary that shows how British society has altered since the early 1970s. The film, directed by David Rust of Lagoon Media, is an independent production supported by CAMRA. It's packed with fascinating footage from the '70s that shows the way in which the arrival of the Big Six national brewers transformed the way beer was made. Wooden casks, coopers and family-run brewers were on their way out. The future lay in filtered and pasteurised beer stored in pressurised kegs. We were all destined to drink Watneys Red and Double Diamond.

Then along came four young beer lovers — all hairy sideburns and flared jeans — who decided to take on the big brewers and save beer with taste and flavour. Unlike another Fab Four, they're all still alive and amazingly hale and hearty despite sinking a gallon or two in the intervening years. They're Michael Hardman, Jim Makin, Bill Mellor and Graham Lees and they explain how they found they had tapped into a great well of discontent among thousands of beer drinkers.

The message from the Big Six at the time was that a handful of grumblers were living in the past and most people were happy to drink keg beer. The founding four proved them wrong. People rushed to join the Campaign for the Revitalisation of Ale as it was first called, swiftly changed to Real Ale on the grounds that it was more manageable and easier to say after four pints of Old Jockstrap.

Hardman and co also found there were an astonishing number of people around with great expertise: they knew how beer was brewed, what happened to living ale inside a cask, how to tap and peg it, and how to measure original gravity. It's hard to believe today, but in the '70s brewers refused to declare the strength of their beers, guarding such information as though it were bars of gold in the vaults of the Bank of England.

One of the funniest moments in the film is the recounting of how CAMRA members would pour beer samples into bottles in pubs and then smuggle them to a friendly technician in the Guinness laboratory, who measured the strength. The early editions of the Good Beer Guide published the original gravities of cask ales and the brewers were forced to give in and declare the strengths of their brews.

The depth of feeling about the disappearance of cask beer as a result of the waves of mergers and closures in the '70s was highlighted when CAMRA, tentatively, organised a beer festival in the Old Flower Market in London's Covent Garden. Would anyone turn up? Would all those casks of beer go to waste?

On the contrary, drinkers queued round the block and the festival was drunk dry. CAMRA members roared off in their Ford Anglias and Hillman Minxes desperate to get extra supplies from bemused brewers who thought they were facing oblivion not great consumer demand.

The film has clips from a '70s BBC documentary, The Philpott File, that covered the rise of CAMRA and juxtaposed it with vast "mega-keggeries", an industrial sprawl of high-rise conical fermenters geared to producing vast amounts of keg ale, brewed without conviction, often controlled by computers, needing neither skill nor passion.

When I joined CAMRA in 1976, it had 30,000 members. Today that number stands at 125,000 and shows no sign of slowing. Last week's Great British Beer Festival attracted an unprecedented clamour for tickets while the number of new small breweries starting up defies a stagnant economy and pub closures.

CAMRA is indisputably the world's most influential single-issue consumer movement. Cynics may point to the fact that the giant global brewers who have replaced the old Big Six brew around 80% of all the beer brewed in Britain.

But the likes of Carlsberg, Heineken and Molson Coors are starting to get the message that cask beer is the only sign of growth in a declining beer market and are taking a belated interest in the sector. Most importantly, the army of small brewers constitute a profound counter-culture, a defiance of the "logic" of the market that says only big brands can win.

CAMRA has made it possible for small brewers to flourish. Britain's great beer culture and heritage has been saved thanks to the campaign's energy and commitment. Do watch the film. It records how the little people stood up to the rich and powerful... and won.

8226 The History of CAMRA, Lagoon Media, one hour 45 minutes, £10. Available from www.camra.org.uk​ or ​ www.britishlocalhistories.com​.