Richard Jeffs came across 64 canisters of film stored in a damp garage in South London, and when he started to go through them he stumbled across a piece of pop history.
The conversation with Scottish television dates from April 30, 1964, according to the BBC, which played excerpts from the nine-and-a-half minute interview on the radio on Tuesday.
It came shortly after the Fab Four's trip to the United States during which they were besieged by fans and watched by a television audience estimated to be about half the country's population when they played The Ed Sullivan Show.
During the interview, Paul McCartney and John Lennon discussed how they came up with their tunes, and Jeffs said it shed light on the songwriting process within arguably the biggest band ever.
When asked how they collaborated, Lennon replied: "Well, you know, it depends. Sometimes we write them on old pianos, anything that's lying around."
McCartney added: "Normally we sit down and try and bash one out. But then again, there's no formula, because he (Lennon) can come up with one day completely finished. We still say we both wrote it, though."
The two also recalled where they first met.
"I was playing at a garden fete in the ... village where I lived just outside Liverpool, playing with a group, and he came along and we met," said Lennon.
Jeffs said the canisters were probably discarded after the tele-recording machine they were made on was replaced by a video machine.
The Beatles recording was on the second can of film that he viewed, he told BBC Radio.
"The first one I opened had got a clip of Cilla Black on it," he said, referring to the British television personality.
"But this was the second one that we took along to get copied, and when they copied it they said 'this must be worth millions'.
"And it is very much like being the man with the million pound note because of course there aren't millions (to be spent) in television and I can't get anyone to play the film in television."
As well as the comments on the songwriting process, Jeffs said the interview was remarkable because it was so relaxed.
"Most of the interviews from this time were them at airports being rushed from one place to the other, and this is a relaxed nine-and-a-half minute interview with them in a studio where they are very happy."
He said he was looking forward to discovering what was in the remaining 62 canisters.
(Reporting by Mike Collett-White; editing by Keith Weir) (Reuters)
Our friend Chris writes:
The interview was recorded in Scotland on 30th April 1964. On Monday this week BBC Radio broadcast a 30 minute show about this interview.
You can download the full 30 minute radio show here :
It is an interesting show.