After the surprises from central banks which rocked markets at the start of the year, the U.S. Federal Reserve will be watched as closely as ever this week to see that it doesn’t stray from its own policy path. The atmosphere will already be tense as the fallout from Sunday’s snap election in Greece settles and concern has grown in some quarters that central banks, which played such a big part in guiding economies through the financial crisis, are becoming less predictable.