In an interview, he told The Sunday Telegraph: “Well, it’s a silly story, because the band wasn’t important back then. Nobody knew who those boys were. But I thought they were great and would have loved to play with them. We were all outside and sat on a heap of wood, and we were all a little stoned. Just for fun, I said, ‘Well, maybe I could play.’ And then John Lennon replied: ‘Ah, Paul’s already bought a bass.’”Days earlier, Paul McCartney had purchased the German-made violin-shaped Höfner 500/1 for £30 (around £600 today), which he played on the Beatles’ early hits, including Love Me Do and She Loves You. However, in 1972, the instrument mysteriously vanished – purloined from the back of a van in the Notting Hill area of London. Now, a charming documentary, McCartney: The Hunt for the Lost Bass, unpacks the twist-filled 51-year quest to reunite Macca with the “Holy Grail of rock ’n’ roll” (as his Höfner has been dubbed).

“Well, I tell you what – that’s hard to imagine. If the Beatles had a fifth member, it might have changed a lot,” he explains in a cheerful sing-song voice. “It’s a question I’ve never thought about.”

“I was at the Top Ten Club nearly every night, and Stuart [Sutcliffe] was playing his Höfner. One day, suddenly there was a second bass. We all knew Stuart was going to leave, but nobody knew who would be the Beatles’ new bass player. From time to time, when there was a complicated song, Paul would pick up Stuart’s bass.”

Following a disagreement with his partner at the time, Astrid Kirchherr (his girlfriend prior to her relationship with Stuart Sutcliffe), he ended up outside the Kaiserkeller near the Reeperbahn drew him in with the magnetic, raw sound of the Beatles. At the time, they were performing alongside another UK act, Rory Storm & the Hurricanes, whose lineup included their future drummer, Ringo Starr.

“It was really refreshing to see those boys onstage. For me, it was mind-blowing. They were special. I knew they were going to go somewhere.” But it wasn’t just their music that inspired him. “At the same time, it was the attitude of those young kids, because they were so different from us Hamburg people, who are very reserved and always careful not to say the wrong word. And those boys were just belting out anything, swearing, and having a great time.”

Regarding his time in Hamburg, Voormann said: “It was very scary for those boys. I mean, George Harrison was only 17 years old. They were far away from home and lonely. They didn’t have any family around, so we became a substitute for that. “We’d say, ‘Let’s go to an exhibition or drive to the beach,’” he continues. “We took care of them because the proprietors of the clubs really sucked the last blood out of them.”

The first time Klaus played bass for the Beatles was at the Top Ten Club… “It was a scary thing,” he says. “I’d walked in, and Stuart gave me the bass and said: ‘Now Klaus, you play.’ I didn’t dare go up onstage. I was sat in front of it with my back to the audience.”

“A bass is such a personal thing,” he says. Sadly, Voormann is no longer able to play his. “I have got problems with my hands, but I’m lucky I can still hold a pen,” he says.