“I may or may not be involved in a case featuring a pop star whose name I couldn’t possibly mention,” he said.

Mr. Oxendale’s reticence to discuss ongoing cases — he won’t even show journalists his office in case they stumble across notes — is evidence of one truth about the world of music copyright: There can be a lot of money involved. Mr. Oxendale takes on around 450 cases a year in which musicians are liable for “thousands, hundreds of thousands, even millions of pounds,” he says. “The duty of care’s quite terrifying.”

Last year, a jury awarded Gaye’s family $7.3 million after deciding that Robin Thicke’s hit “Blurred Lines” copied one of his songs. (Mr. Oxendale was involved in the case, though he won’t say how, and says the verdict was appalling. “Those songs only share a groove. A jury can say the sky is green, but that doesn’t mean it is.” He expects it to be overturned on appeal).

Mr. Oxendale got into the profession by accident. He grew up in Hull, a port city in northern England, and was set to become a music teacher until he answered an ad for an “image-conscious keyboard player” (“I had a wispy beard”) and soon found himself touring America with glam-rock acts. He thought he was set for a life of private jets and five-star hotels, but then, just as suddenly, punk came along.

“I couldn’t get arrested,” he says. “I was a longhaired rock ’n’ roll fossil playing in pubs on Friday nights to get money.” One day, he visited a publishing company to sell them some songs when its head of legal affairs spotted him. “He said, ‘Oxendale, you’ve got a music degree, haven’t you? Can you do me a report?’ And I was absolutely skint so said ‘yes.’ I wrote seven pages in longhand. I didn’t know anything about copyright. It must have been absolute garbage.”