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The exposing of five University of Cambridge graduates as Soviet spies remains one of the most fascinating stories from the Cold War.

The members of the so-called ‘Cambridge Five’ spy-ring were all from privileged backgrounds and firmly part of the British establishment.

So what motivated them to side with Stalin?

Louise Hulland and historian Dr Sean Lang have been finding out.

(Photo of Cambridge spy Kim Philby in 1955. Credit: Harold Clements/Hulton Archive/Getty)