Andy Coulson today told the hacking trial he was aware of the "irony" of his newspaper exposing an affair by a senior politician while having a long-running extra-marital affair himself.

A front-page story in Mr Coulson's News of the World in 2004 revealed that the then Home Secretary, David Blunkett, was in a relationship with a married woman.

The story was obtained by the News of the World by intercepting Mr Blunkett's messages to the publisher Kimberly Fortier and 300 hacked messages were found in a safe at the London headquarters of its owner, News International.

In earlier evidence Mr Coulson told the case that he was "shocked" to be told by his chief reporter, Neville Thurlbeck, that he had hacked the messages, but published the story anyway because he thought it was in the public interest.

Evidence presented to the court has revealed that between 1998 and 2006 while their newspapers were exposing extra-marital affairs Mr Coulson and his fellow redtop editor, Rebekah Brooks, were having an affair while married to other people.

Asked by Clive Goodman's lawyer, David Spens QC today about his decision to run the Blunkett story despite its illegal origin, Mr Coulson told the Old Bailey: "I regret the decision I made."

Mr Coulson went on: "This is a story about someone's private life, and given what was going on in my own private life the irony of it is not lost on me.""Pure hypocrisy, isn't it?" asked Mr Spens.

Mr Coulson repeated to the jury: "The irony of it is not lost on me."

He confirmed that following publication of the front-page story, headlined: "Blunkett's Affair With A Married Woman", no disciplinary action was taken against Thurlbeck.

Asked if he had had a conversation with him about the story after publication, Mr Coulson replied: "Not that I remember."

He agreed that he had not launched an internal inquiry into the hacking or raised the issue with the Press Complaints Commission.

Mr Spens asked the journalist: "So the story which is a product of phone hacking is out but nothing seems to be happening within your organisation to prevent it happening again?"

Mr Coulson replied: "The story had been brought to me by the chief reporter... and I made the decision I made - and I have told the court I think it was a mistake."

Mr Coulson, who edited the News of the World between 2003 and 2007, denies conspiring to intercept communications. The case, which began in October, continues.