A Goldman Sachs exec has dealt a deeply embarrassing blow to the firm by quitting in an open letter in which he lambasts the working environment as 'toxic and destructive'.

Greg Smith, an executive director who has worked at the New York-based investment bank for 12 years, claimed it is more interested in making money for itself than its clients.

In a scathing resignation letter published in the New York Times on Wednesday, he reveals staff have so little respect for clients, they call them 'muppets' and talk of 'ripping eyeballs out'.