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And now another chance to hear the BBC's security

correspondent Gordon Carrera's unique insight into the activities of

Britain's secret intelligence service.

I can feel the adrenaline sort of pumping through

and I think back to some of the things that I, many others, were required to do.

Well there have been other times in my life where I have been involved

and death, yes. But I can't talk about that.

MI6, a century in the shadows.

Part 2, heroes and villains.

Vienna 1950, a city divided into four by occupying powers,

a Cold War crossroads teaming with spies.

In his early 20s, Anthony Cavendish was then the youngest officer

recruited into the secret intelligence service, MI6,

his task running agents, providing information on the enemy.

We have an arrangement in one of the beer sellers

in the Russian sector where one of the musicians was known to us and was

helpful to us and where I used to have meetings with an agent.

I would go to the Russian sector and go down the steps into this beer seller

and when the musician saw me arriving, if all was friendly and quiet

...