Unseen footage of Kim Philby talking about life as a double agent

The BBC has uncovered previously unseen footage of one of Britain's most infamous spies talking about his work as a double agent.

Following his defection to the Soviet Union, Kim Philby gives a seminar to East German spies on how to succeed at espionage.

It is the only known footage in which Philby discusses his betrayal of Britain.

Gordon Corera reports.