The fascinating film, shot behind the scenes at the festival by award- winning New York film director Murray Lerner, is certain to become an instant classic. It shows the last stage performances of Jimi Hendrix and Jim Morrison of The Doors, as well as music from The Who, Free, Joni Mitchell, The Moody Blues, Miles Davis, Jethro Tull and many others.
But, much more than this, it exposes the hypocrisy among both audience and performers in betraying the hippie ethos. Supergroups who preached love and peace to the 600,000-strong audience refused to go on stage until they were paid in cash.
The film, to be screened on BBC2 over the August bank holiday, shows the organisers counting out more than pounds 3,000 for the American group Chicago to persuade them to go on.
The then cult singer Tiny Tim preaches a hippie sermon from the stage, exhorting the audience to "share with your neighbour". Backstage the cameras record an agent saying: "Tiny Tim's going on but we had to give him the money first. He won't sing with his ukelele without the money."
Among many memorable moments is a young Joni Mitchell having her microphone snatched by a member of the audience protesting at the pounds 3 cost of tickets.
A tearful Mitchell berates the audience, telling them they don't understand artists - "We put our lives into what we do, you should show us respect" - and delivering the Mitchellesque insult that they are "behaving like tourists".
In fact, they behaved far worse. The film shows that Britain's Woodstock suffered a near riot. Hippies, unwilling to pay the admission price, tried to knock down a fence and attack a policeman, and did attack a police dog.
The organiser of the festival, Ricky Farr, son of the Thirties boxer Tommy Farr, yelled at a section of the audience that they were pigs and instructed his security men: "If they try and get in through the mud they should go out through the mud, but on their chins."
But Farr was canny enough to avert a possible riot by letting protesters come on stage to make their points. One of those urging that the festival be free, says: "This festival business is becoming a psychedelic concentration camp. What is all this peace and love shit when you've got police dogs out there?"
The dated language can be as intriguing as the music. At one point the organisers, complaining about the agents, refer to "the mohair-suited Brylcreem brigade."
And an Isle of Wight islander claims darkly that "behind the hippies are black power, and behind black power is communism".
The most curious aspect, however, is that the two-hour film has never been shown before.
Lerner in fact shot 175 hours, and both as a sociological record of the last great shout of hippiedom and as a record of star performances, one would have expected it to have been in constant demand.
Speaking from New York last week, he said: "I have been obsessed with this film for 25 years, and it has been an incredible frustration for me that no one has wanted to back it until now. The film industry just weren't interested.
"I was trying in the film to show the realities behind the myth, the complexity of ideologies that say one thing and do another."
In fact, by the end, while some of the hippies behave violently and selfishly, it is Farr the businessman who shows himself to be a true follower of the creed.
The festival, with one of the best line-ups the world has ever seen, went bankrupt. And in a poignant address from the stage, Farr says: "We've lost everything, but when I say everything I only mean money. We are possession- wise more naked than any of you because we are now open to creditors.
"But we don't care about that. The very fact that you are sitting there and we have been able to provide this is worth more than money can buy.
"And all I can say to you is, go home with some love and some peace."
`Message To Love' will be shown on BBC2 on Saturday 26 August.Reuse content