When Keiron Marshall was 15, he found his way out of a desperate situation with help from an unexpected source: Eric Clapton. The guitar great was host at the first gig Marshall ever went to, and he was joined on stage by Gary Brooker of Procol Harum, The Who’s Pete Townshend and Beatle Ringo Starr. Since then, London’s music scene has been a liferaft for Marshall, a musician who now runs a group of small concert venues with his wife. Growing up in south London, he’d endured racial slurs and regular beatings because of his Pakistani heritage. His uncle was killed in a racially motivated attack; his mother was a heroin addict. But the music scene they know and love may soon be unrecognizable because of the coronavirus pandemic, which has plunged the U.K. economy into its worst recession on ...