A senior Scotland Yard detective has expressed his "extreme regret" that he did not act to reopen police inquiries into phone hacking two years ago.
Despite fresh allegations that thousands of public figures had been targeted, Assistant Commissioner John Yates ruled in July 2009 that there was no new evidence.
He has come under vociferous criticism from MPs over his stance and has been called on to give evidence to an ongoing inquiry by an influential Commons committee.
The initial police investigation led to the jailing of News of the World royal editor Clive Goodman and private investigator Glenn Mulcaire.
But it was accepted that they were an isolated case.
Speaking after this week's revelation that the mobile phone of murdered school girl Milly Dowler had in fact been among those targeted, he said: "We are all extremely shocked by it and it is a matter of massive regret we didn't deal with it earlier."
In an interview with the Sunday Telegraph, he said: "My byword has always been you look after the victims and the job will always resolve itself.
"I always put the victim first but here I didn't follow my principle and that is my greatest regret."
He told the newspaper: "I didn't do a review. Had I known then what I know now, all bets are off. I would never have reached this conclusion.
"I am accountable and it happened on my watch and it's clear I could have done more.
"I have regrettably said the initial inquiry was a success. Clearly now that looks very different."
The entire scandal had been "a very damaging episode" for the Metropolitan Police, which now faced a task to rebuild public confidence, he said.
Announcing his decision in 2009, Mr Yates declared: "No additional evidence has come to light since this case has concluded.
"I therefore consider that no further investigation is required."