The decision to expose David Blunkett's affair with a married woman in the News of the World based on an intercepted voicemail was a "mistake" but showed "the system worked", Andy Coulson told the hacking trial.

The former News of the World editor who had an on-off affair with his co-defendant Rebekah Brooks, added: "The irony is not lost on me."

Coulson was being cross examined by former NoW royal editor Clive Goodman's defence lawyer during his sixth day giving evidence at the Old Bailey.