Almost 55 years ago, Michael Eavis hosted the first of his legendary music festivals. In 1970, the BBC visited his Somerset dairy farm to find out what made it unique.

"I think this is the quickest way of clearing my overdraft," said Michael Eavis on 18 September 1970 when he was asked on the BBC why he had booked glam rocker Marc Bolan to perform in his field. The dairy farmer was being interviewed on his Somerset farm, as he sat on a newly-made makeshift wooden toilet, the day before the opening of what would go on to become one of the most famous and celebrated music festivals in the world.

The Glastonbury Festival in the decades since has evolved into a vibrant, sprawling cultural extravaganza which draws the biggest names in the music business: Neil Young, Olivia Rodrigo and The 1975 are all due to headline this year. Tickets sell out within minutes, and thousands of revellers from all over the world are expected to descend on the farm's rolling fields this week for the chance to experience the festival's mix of music, dancing and fellowship.

But the first festival was a more modest affair and was partly driven by Eavis's need to keep his family's farm afloat. "It's a means of staying in the business," he told BBC reporter John Norman a few weeks before the first festival began. "There are people selling up all the way round here, about a dozen sold up in the last five years, and we've got to do something because farming is such a dead loss."

Eavis's family had been farming the land in Somerset, UK for well over a century. Born in 1935, he was the eldest of five siblings, and his parents, a Methodist preacher and a headmistress, had instilled in their children a strong sense of social responsibility. But even as a child, Eavis was obsessed with pop music. At boarding school at the age of nine he was punished for smuggling in a wireless so that he could listen to Radio Luxembourg at night. As an adult, despite dairy farming being tiring and time-consuming work, he still found time to indulge his passion, playing pop music to his cattle while they were being milked. "I invented a sound system, and it was all tied up with string and stuff, and wired it into my player in the dairy and it was fantastic sound. So, I played [The Kinks' song] Lola to the cows day after day and I really enjoyed it," he said on the BBC's Witness History podcast in 2015.

The farmer was convinced that the cows enjoyed his music selections, too. "They do like the music very much," he told the BBC in 1970. "We have it in the stalls and they are used to it. And it seems to be proved to me that it does, in fact, affect the yield because I had a relief milker coming in – I had to do the milking while I was doing the show – and the first day he didn't want the wireless on, and I was 10 gallons down on production."

Eavis had been running the farm since he was just 19, when his father died of cancer. But along with taking over Worthy Farm, Eavis had also inherited its sizable overdraft. "If you are just stuck with a farm and you are scraping along on an overdraft which it is almost impossible to meet the interest for, you've got to use your head and think of something else to do," he told Norman.

It was in the summer of 1970, when the single Lola was released, that inspiration came to him. He was attending, with his future wife Jean, the Bath Festival of Blues and Progressive Music, and he was bowled over by the event's "absolutely marvellous atmosphere".

"The Sun was shining, people looked fantastically beautiful, mainly hippies in great clothes and flowers in their hair, all that sort of thing, because it was the peak........

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