Magnum was established 70 years ago by a small group of the 20th century’s most famous photojournalists — Henri Cartier-Bresson, Robert Capa, George Rodger and David ‘Chim’ Seymour.

Drawn from archival holdings, this exhibition revisits some of the Guardian’s and The Observer’s most distinctive Magnum commissions. It includes a 1948 vintage print of Picasso and his son, Claude, taken by Robert Capa, and Philip Jones Griffiths’ series about the 1960 Ban the Bomb march from Aldermaston to Trafalgar Square.

The archival material illustrates the evolution of the standalone picture-story, a Fleet...