"I SWEAR by almighty God to tell the truth, the whole truth, and nothing but the truth. Only joking!" Does speaking on oath make any difference at all?

Despite the oaths sworn, there appears to have been some careless­ness with the truth at the Leveson inquiry. Two former Prime Min­isters, for instance, claim that Rupert Murdoch lied in his evidence.

The media magnate claims never to have asked a Prime Minister for anything, but John Major says that Mr Murdoch asked him to change the Conservative stance on Europe, or his papers would withdraw their support. Mr Murdoch also claims that Gordon Brown "declared war" on him in a phone call; but both Mr Brown and the Cabinet office re­cords deny that such a phone call took place.

They cannot all be right. And then the former editor of The Sun, Rebekah Brooks, said that her paper had the Browns' permission to print a story about their son. Mr Brown denied this, and was supported by the NHS, who said that the paper got the story from an insider at the hospital.

But Mr Brown also said that he had never instigated or discussed any personal attacks on Tony Blair, which left many in the press corps aghast.

Meanwhile, George Osborne and David Cameron said that they had enjoyed countless dinners, Christ­mas Days, phone calls, text mes­sages, and private meetings with the News Corp hierarchy, but we must understand that they amounted to nothing in terms of payback. LOL was the general response - which, as Mr Cameron learned from his own chummy text exchanges with Mrs Brooks, does not mean "Lots Of Love", but "Laugh Out Loud".

So, what now for the oath? Does it possess the moral force to turn a liar into a teller of truth? The Leveson inquiry suggests that it does not, and perhaps we are not surprised.

It is one of life's ironies that the traditional court oath is taken with the hand of the witness placed on the Bible - perhaps the only book explicitly to reject the practice of oath-taking. "Simply let your yes be yes, and your no, no," Jesus said. "Anything beyond this comes from the evil one." It makes sense. If you struggle with truth in the office, you will struggle with it in court.

The boundaries between forget­fulness, self-deception, and lying are not always clear. Survival strategies that were adopted by us when young create a brain hard-wired to deceive - a skill we take into adult life. We invent what we need to, and retain a terrifying capacity to believe our inventions. And the rich, it seems, are the same.

The Leveson inquiry is an inquiry into the culture, practice, and ethics of the press. It is the great and the good who have been invited to give their version of events - and it is the great and the good who have ensured the very public death of the oath.