A builder could be £10,000 richer after finding papers in a skip that included sketches Sir Paul McCartney commissioned for his psychedelic piano.

Andy Clynes, 54, from Oldham, was overseeing a development at a mill near Manchester when the papers were thrown out with other waste.

He took them out of the skip and stored the papers in a box in his loft for around 20 years until deciding recently to see what they are worth.

The paper listing the commission for Sir Paul McCartney (Omega Auctions/PA)

An auction house is now selling the highlight of the find, the sketches and designs for the Beatle’s so-called “magic” piano.

More of the papers from his find will go under the hammer in a separate sale later this year at Omega Auctions, with the total expected to fetch £10,000.

Mr Clynes, 54, told the PA news agency: “I picked them out of the skip.

“The case burst open as it was thrown in. It was raining and I just picked up what I could.”

I imagine there was a lot more there but it was damaged.”

The papers document a handwritten list of commissions for 1960s art collective BEV.

The design for Sir Paul McCartney’s piano (Omega Auctions)

They include commissions for The Kinks – the collective worked on their album cover Sunny Afternoon – Lord Snowdon, Guinness heir Tara Browne and Sir Paul.

Collective member Dudley Edwards painted the psychedelic motifs on to the star’s piano in 1967.

Mr Clynes, a buildings site contract manager, picked up the papers around 1999 while converting a mill into a wine bar.

To this day, he does not know why they were there.

“It could have been an art studio at some time or another,” he said.

“I’ve had them for 20-odd years. You put things away and forget about them and then something triggers your mind.

“I haven’t planned what I’ll do with the money yet but I was surprised about the value.”

One of the items included in a list of commissions says “to paint Paul McCartney’s piano”.

Mr Clyne said: “I Googled ‘Paul McCartney’s piano’ and when I looked at the drawing it was very similar.”

Auctioneer Paul Fairweather described the papers as a “rare find”.

“It’s fantastic that such an important archive was recovered and even better for our vendor that it should prove a lucrative decision to save them from the skip,” he said.

“The designs of BEV encapsulate the optimism, excitement and free spirit of collaboration that ensures that the late 1960s endure in the popular consciousness even to this day.”

The sketches and designs for Sir Paul’s piano are expected to fetch up to £2,000 in the Beatles vinyl and memorabilia sale at Omega Auctions on March 24.

The rest of the papers will be auctioned later this year.