Activist investors used to target only the most polluting or most socially repugnant companies. But banks are now squarely on their hitlists and the pressure is likely to ratchet upwards.

By reputation, activist investors are terrifying carnivores, devouring old habits and spitting directors out at the end of short periods of turmoil. Typified by hedge funds, they may try to dictate terms to companies, exemplified by the pressure put on Deutsche Borse last year to withdraw its takeover bid for the London Stock Exchange.