Gadgets and Green Ink

BBC security correspondent Gordon Corera looks inside Britain's Secret Intelligence Service. He talks to MI6 chief Sir John Scarlett, senior intelligence officers, agents and diplomats as well as their former arch enemies about the shadowy world of espionage.

Charting the early years of MI6, founded by Sir Mansfield Cumming - an eccentric and formidable figure known as 'C', who signed his name in green ink - the highs and lows of the two World Wars and details of some of the gadgets that any self-respecting agent could not do without.