Nick Drake's treasured secret tape up for sale

When Nick Drake died from an overdose of anti-depressants aged 26, the now acclaimed folk musician believed almost no one was interested in his work. Among his last wishes he bequeathed a reel-to-reel tape of his first proper recording to somebody he knew did care – Beverley Martyn, a leading figure of the early 1970s UK folk scene who came to view him as her "younger brother".

Martyn, who made two albums with her ex-husband, the late folk legend John Martyn, cherished the tape, playing it a lot but at the age of 67 and in failing health decided it was time to part with it.

The six songs, recorded before Drake began work in 1968 on his seminal Five Leaves Left album, are to be sold by London auctioneers Ted Owen & Co. The tape has been valued for insurance purposes at £250,000.

It features Drake playing either guitar or piano and singing some of the songs that brought him posthumous fame in the 1980s and 1990s, such as "Fruit Tree", "Saturday Sun" and "Cello Song". His music won him fans such as Brad Pitt, who presented a 2004 documentary about Drake, and influenced artists as diverse as Belle & Sebastian, the Cure, and Paul Weller.

The tape was "a wonderful thing – because it's him", Martyn said. "He was young, he sounds full of fun, he sounds light and his guitar playing is absolutely excellent. It really shows that he didn't need to have this whole layer cake of strings.

"Okay, the strings were great on the album, but this is just him and it makes it more personal."

The making of all three of Drake's albums was a problematic process. He argued with the record company about the arrangements on the first, appears to have capitulated on the jazz-influenced second record before getting his way on the third – by which time his disillusionment with the music business had begun to affect his work. All three sold poorly and Drake was dropped by his record label, and he died in 1974.

Martyn said she had tried to convince him that his talent would eventually be recognised. "I constantly had to reassure him that his music was great and he should think of himself not as being popular now but being popular in the future," she said. "I said, 'One day everyone is going to know who you are, these songs are good, these songs are great, you are an original', but he said, 'No, no.'"

Martyn, who released an album this year called The Phoenix & The Turtle, featuring a song she wrote with Drake, appeared at the Monterey International Pop Festival in California in 1967, toured with Simon & Garfunkel in the US, and performed with Richard Thompson, Ralph McTell and Jimmy Page. But she made little money and was not paid for her work on the albums with her ex-husband. The money went to John and she does not receive royalties.

"I don't get a proper pension," she said. "I'm not well: I've loads of things wrong with me. I don't want this tape to get lost or get into the wrong hands if anything happens to me. I've cared for this [tape], I've loved it and I've had my time with it.

"Someone else should be able to enjoy it and I know there are people out there who are made for him."