The head of the German Bundesbank, Jens Weidmann, is concerned the Irish promissory note deal stretches the ECB's rules against providing direct monetary finance to eurozone states to breaking point.

He says the ECB will re-examine the issue and "has to make sure that its actions are in conformity with its rules and statutes".

He said: "I'm very concerned about monetary policy being too closely intertwined with fiscal policy and crossing the line to monetary financing."

"Once you cross a certain line, setting a precedent, it's very difficult to come back and argue against the next similar transaction," he added.