Martin Parr is something of a cottage industry in Britain. The photographer’s name, likeness and work have adorned M&M’s, leather jackets, soccer scarves and Bombay Sapphire gin, among other things. He currently has solo exhibitions in Bogotá, Manchester and London and has published more than 100 books. He was also the president of Magnum Photos from 2013-17.

Yet for all his success, according to “Only Human,” the new monograph by Phaidon Press that accompanies his show at the National Portrait Gallery in London, Mr. Parr almost wasn’t elected to Magnum in the first place.

When he first tried to gain full membership to Magnum, in 1994, his path was nearly blocked thanks to the blunt criticism of photojournalist Philip Jones Griffiths. In a letter opposing Mr. Parr from joining, Mr. Griffiths wrote, “Let me state that I have great respect for him as the dedicated enemy of everything I believe in and, I trust, what Magnum still believes in.”