New details of one of Britain's biggest spying scandals in which Guy Burgess and Donald Maclean - two members of the so-called "Cambridge Five"- defected to the Soviet Union have emerged in newly-released secret files.

Over 400 secret files from MI5, the Foreign Office and the Cabinet Office are being released to the National Archive.

There are also files that relate to other operations, suspected agents and individuals under surveillance.

Robert Hall reports.