Nemat Shafik, an IMF deputy managing director, yesterday stressed the value of central banks' "open mouth operations" in implementing policy and moving markets.

Speaking in London yesterday, Shafik acknowledged the "previously boring and highly secretive world of central banking" had moved into the limelight. This increased attention on its activities means communications has become central bankers' most important tool, she said.

"Central banks often don't have to buy anything to move markets –