Yard chief: I only heard Milly's phone had been hacked from the media

A senior Scotland Yard officer today expressed "great regret" that police had failed to uncover evidence that Milly Dowler's phone had been hacked by the News of the World.

Assistant commissioner John Yates, one of the officers at the centre of the hacking inquiry, said he only knew that Milly's phone had been one of those hacked when he read about it in the media.

In a letter to Home Affairs select committee chairman Keith Vaz he said it was a matter of "huge concern" that the matter was not uncovered earlier.

Mr Yates, who carried out a one-day review of the evidence in July 2009 and ruled there were no new grounds to re-open an inquiry, said he had based his decision on "detailed briefings".

He said this view was supported by the Director of Public Prosecutions, Keir Starmer QC, who had simultaneously ordered an urgent examination of the material and later concluded it would not be appropriate to launch a new prosecution.

Mr Yates also issued an apology to the Mayor today, saying he briefed Mr Johnson on his findings "in good faith".

Sources told the Standard that at a meeting to discuss the original phone hacking investigation Mr Yates had "looked Boris in the eye" and told him there was "no one more to investigate".

In a letter to the Mayor today Mr Yates wrote: "I briefed you on the basis of what I had established at the time. The responses I gave you were in good faith.

"The reason that the new investigation has been opened and the situation has subsequently changed is that in January 2011 News International have begun to co-operate properly with the police. This was not the case beforehand. It is a matter of great regret that this co-operation was not forthcoming earlier. Had it been, my decisions and my briefing to you would inevitably have been very different."

His comments come as Met Commissioner Sir Paul Stephenson was expected to face a grilling from the Metropolitan Police Authority on Thursday. He faces calls for an apology.

Labour member Joanne McCartney said: "When I asked John Yates in January about the new allegations in the media he said they were new to the media but not to the police. That gave the impression that the police already knew about these claims.

"I think the Met now has to give a full account of the actions they took during the initial inquiry and the review."

Dee Doocey, the Lib-Dem London Assembly policing spokeswoman, said: "I have for many months been saying that the relationship between the Met's senior executives and those of News International has been far too cosy.

"If the Met was investigating a private company there would be no way that senior officers would be having dinner with the company's chief executive."