Milly Dowler's mother felt "euphoria" when she finally got through to her missing daughter's voicemail after a private detective deleted some of the messages, the press standards inquiry heard today.
Sally Dowler's hopes were falsely raised when News of the World investigator Glenn Mulcaire erased a number of the 13-year-old schoolgirl's voicemails, the Leveson Inquiry was told.
David Sherborne, counsel for the Dowler family and 48 other alleged victims of press intrusion, said: "Perhaps there are no words which can adequately describe how despicable this act was."
The Dowlers, who will be the first witnesses to give evidence to the inquiry, suspect that their own phones were also hacked, the hearing was told.
Mr Sherborne said the Dowler family were also subjected to "terrible intrusion" when they retraced the route Milly was walking in Walton-on-Thames, Surrey, when she was abducted in March 2002.
The lawyer said they intended this as a "private moment" which would help them to come to terms with their daughter's disappearance.
But they were photographed and their picture appeared in the News of the World under the headline The Longest Walk.
Mr Sherborne said Mulcaire committed an act of "cruelty and insensitivity" in hacking Milly's phone.
He said: "Mr Mulcaire, acting in the course of his work for the newspaper, had deliberately accessed and listened to the missing 13-year-old's voicemail.
"And worse still, he had even deleted some to ensure that there was room for waiting voicemails to come through to their otherwise full mailbox."
He went on: "Mr and Mrs Dowler will tell you in their own words what it felt like in those moments when Sally, her mother, finally got through to her daughter's voicemail after persistent attempts had failed because the box was full, and the euphoria which this belief created, false as it was unfortunately.
"Perhaps there are no words which can adequately describe how despicable this act was."
Mr Sherborne said it was legal action such as that launched by actress Sienna Miller which forced the practice of phone-hacking to be "taken seriously" by the police.
The actress, who has been given "core participant" status in the inquiry, launched a civil battle which became something of a catalyst for a series of claims made by numerous individuals against the News of the World, he told the hearing.
"It was individuals like Sienna Miller who were prepared to take on the News of the World, unlike those in Government or from other areas," he added.
"And it was Sienna Miller and others' actions which forced the phone-hacking scandal to be taken seriously by the police."
While many of those targeted by the tabloid were celebrities, some were simply connected to high-profile figures," he said.
Others included individuals such as Sara Payne, whose eight-year-old daughter Sarah was murdered by paedophile Roy Whiting in West Sussex in 2000.
Ms Payne, who worked closely with the News of the World to campaign for better child protection laws after her daughter's death, was "devastated" to discover that her phone may have been hacked into on behalf of the disgraced tabloid, following the newspaper's closure.
"One of the cruellest twists to the whole story is the fact that one of the (newspaper's) most prominent targets had also been one of its most prominent supporters," Mr Sherborne said.
The revelation came after the red top published a letter from Ms Payne in its final edition which thanked it for its support.
It was a "sickening post-script" and "perhaps a new low amongst a wealth of lows for a newspaper whose former glory has been so befouled by its cultural dependency, it seems, on dark arts which sadly give journalism and journalists a bad name", Mr Sherborne said.
Besides those in the public eye, others were targeted for their access to the rich and famous, the inquiry was told.
"They were people whose crime was simply working for well-known people," the barrister added.
He cited the cases of model Elle Macpherson's former adviser, Mary-Ellen Field, and an individual referred to only as HJK to protect the identity of a famous figure with whom HJK began a relationship.
He told the hearing that Ms Field was blamed by Macpherson after damaging stories about her private life appeared in the Press.
She was sent to a clinic in America because Macpherson believed her refusal to accept responsibility for the articles was sparked by personal issues, namely that she had to care for her disabled son and had "problems with alcohol".
Despite being sent home from the clinic, Ms Field "was in any event sacked by her employer", the hearing was told.
Meanwhile, Mr Sherborne said HJK was believed to have had their phone hacked in the summer of 2006 - around the time when HJK was approached by a journalist claiming to be from another newspaper group wanting to publish a story about HJK's "embryonic" relationship with the well-known figure.
HJK's concerns increased after being diagnosed with a "serious illness", the lawyer said. Soon after this, a photographer who had been following HJK "jumped out" and took a picture.
The effect on HJK was "profound", Mr Sherborne added.
Mr Sherborne said the whole of the British press was standing in the dock as Lord Justice Leveson's inquiry got under way, adding that he wanted to highlight "systematic, flagrant and deeply entrenched" abuses over several years.
He said the charges ranged against newspapers included: phone hacking, "blagging" private information through deception, blackmailing vulnerable or opportunistic people into breaking confidences about well-known people, intruding into the grief of crime victims and hounding celebrities, their families and friends.
"We are here not just because of the shameful revelations which have come out of the hacking scandal, but also because there has been a serious breakdown of trust in the important relationship between the press and the public," he said.
"It is the whole of the press, and in particular the tabloid section of it, which we say stands in the dock, at least metaphorically so - and certainly in the court of public opinion."
The lawyer said certain British newspaper editors were "members of the 'see no, speak no, hear no evil' brigade" and accused them of "complacency" about the problems in their industry.
"The press is a powerful body. They have a common interest in a self-serving agenda. Why wouldn't they, after all?" he told the inquiry.
"This is about survival and they have lobbied hard to try and push their agenda through the pages of their own highly-influential newspapers to influence politicians with the sole objective that there should be less rather than more restriction or regulation, and that if this was so journalism would be even better."
Mr Sherborne said the volume of calls made by Mulcaire or which came from "within News International" were part of a "routine plundering" of voicemails.
He referred to counsel to the inquiry Robert Jay QC's description of the News of the World's phone hacking activity as "a thriving cottage industry".
"The evidence demonstrates not so much a cottage industry, as Mr Jay called it, but rather an Industrial Revolution, a culture change, we say, away from proper old-fashioned journalistic activity," Mr Sherborne said.
"The police say in the 11,000 pages of Mr Mulcaire's notebook it looks as if there is evidence of well over 2,000 tasks assigned to him in the four years to which the notebooks relate," he added.
"That means potentially 500 plus stories each year from this single source which means, on such a calculation, that there were possibly 10 stories in each edition of the News of the World which were the product of phone hacking alone, even leaving aside the other dark arts practised by the newspaper."
While he recognised this was "speculation", he added: "There is other evidence which suggests higher figures."
"It is hard not to conclude that the very foundations of this most popular newspaper throughout these years were built on manifestly unholy and indefensible ground.
"And, if the newspaper was receiving such an endless stream of stories, and a significant number of journalists were involved, then it must surely raise questions about who knew what and at what level."
Mr Sherborne said freedom of speech was "only one part of the equation" and had to be balanced against the right to respect for private life.
"The respect which is given to an individual's privacy is as much a mark of a tolerant and mature society - as we like to believe ours is - as a free and forceful press," he said.
He accepted it might be a different story in the case of people who "expose their entire life to the press and trade off that" - but said examples of this were "few and far between".
Mr Sherborne cited the case of former Formula 1 boss Max Mosley, who won £60,000 in privacy damages at the High Court in 2008 over a News of the World story claiming he took part in a "Nazi orgy", something he has always denied.
He said the newspaper's revelations about Mr Mosley's sex life could not be removed from the public domain once they were aired.
"Let's be honest, who can look at him without thinking about what he chooses to do with other consenting adults in private?" the lawyer said.
"And then stop and ask yourself this: is this something you really feel you're entitled to know about? Whatever your answer, you do know it. And once you know it, it's too late."
He said Mr Mosley was faced after the story was published with a choice about whether to "retreat and accept this humiliation" or to "prepare himself for a full-blown trial, with all the added embarrassment that this would cause".
Mr Sherborne said the ex-F1 boss - whose father was Oswald Mosley, former leader of the British Union of Fascists - would tell the Leveson Inquiry that the News of the World "preconceived" the Nazi angle for its story and tried to make the facts fit it.
The lawyer said a distinction had to be drawn between the public interest and matters that were of interest to the public.
He told the inquiry: "I am not advocating boring newspapers. Don't get me wrong, I like to read about gossip. Most people do.
"But just because I like to doesn't mean that I should, or that newspapers should be able to invoke that curiosity, that prurient interest in such matters, to defeat an individual's wish to maintain respect for the boundaries of their private life."
And the barrister raised questions over whether press intrusion could be blamed on a selection of reporters who were left to "run amok with the company chequebook" or whether it was condoned in the upper echelons of newspapers.
He said: "Can it really be sensibly argued that this is a simple case where checks and balances were not properly observed and that a handful of rogue journalists were allowed to run amok with the company chequebook?
"Or, rather, was such activity the systematic and deliberate employment of unlawful methods encouraged or condoned at higher positions in the newspaper for the purposes of obtaining stories about the private lives of individuals, the very lifeblood on which this newspaper prided itself?"
The inquiry has heard that Mulcaire's notebooks, which were seized by detectives in 2006, suggest that at least 27 News of the World employees other than Goodman commissioned him to hack phones.
But today Neil Garnham QC, representing Scotland Yard, said police could not confirm that all 28 had worked for the former red top.
"It isn't correct to suggest that a fair inference can be that they were all News of the World employees," he told the inquiry.