Deep in his managerial lair, Stuart Camp presses a button on a remote control and waits for the magic to happen.

He’s in his lavishly-appointed, state-of-the-art new Grumpy Old Management office in Holland Park, West London, surrounded by the spoils of his 10-year association with the one and only Ed Sheeran. Every wall is adorned with various multi-platinum discs for Sheeran and the many artists he has written songs for or with (from Taylor Swift and Eminem, to DJ Snake ...