Files released this week revealed the jokes were collected from letters steamed open by agents, from spies on the ground and wiretapped phone calls.

The gags were scrupulously collected and filed and dispatched to Bonn, much to the delight of civil servants.

"It was our biggest hit among our superiors," said one unnamed BND spy. "The Chancellery and the ministries couldn't wait for the file to have a laugh at those on the other side."

BND officials said the jokes gave valuable insights into the way East Germans were thinking about their government.

Joke reports prepared for the BND leadership and its political masters always contained analysis of the situation behind the Iron Curtain.

One report read: "The GDR leadership believes the population is resilient and ready to make sacrifices but it is prepared to take tough action if necessary to prevent 'Polish conditions'."

Telling jokes was a risky business for the citizens of East Germany.

The Stasi secret police turned one third of the country's 17 million citizens into informers for the state.