Top executives at Rupert Murdoch's News of the World "must have known" about phone hacking, which was so widespread that three senior news editors have admitted their involvement, British prosecutors say.
They also alleged on Wednesday that former Murdoch protegee and ex-News of the World editor Rebekah Brooks authorised large sums to be paid to public officials for information while she edited the tabloid's sister daily, the top-selling Sun.
The long-awaited trial is the first time that criminal charges have been put to alleged key players in the hacking scandal, which sent shockwaves through the British establishment.
Brooks, 45, is among eight defendants facing charges ranging from phone hacking to bribing officials and concealing evidence. All the defendants deny the allegations against them.
She took detailed notes as she sat in the glass-fronted dock on Wednesday next to Andy Coulson, her successor as editor of the News of the World who went on to be communications chief for Prime Minister David Cameron.
Opening the prosecution case at London's Old Bailey court, lawyer Andrew Edis said there was a wealth of evidence that hacking was widespread at the News of the World.
In a surprise announcement, he revealed that three former newsdesk editors - Greg Miskiw, Neville Thurlbeck and James Weatherup - had all pleaded guilty ahead of the trial to conspiring to illegally access voicemails.
While this did not necessarily implicate Brooks and Coulson, Edis said the guilty pleas revealed that "there was a conspiracy which involved a significant number of people, and it was quite a substantial conspiracy".
"And that may help you to decide now," he told the jury. "Because those names, they knew. So who else knew?"
He argued that Brooks and Coulson, along with the paper's former managing editor, Stuart Kuttner, must have known about hacking, not least because they controlled the budget, and obtaining hacked information cost a lot of money.
Private investigator Glenn Mulcaire, who has previously been jailed for phone hacking, was on a contract worth an estimated STG100,000 ($A170,300) a year to dig up stories for the News of the World.
"What you are going to have to consider is whether these people were doing their jobs properly, in which case we say they must have known what they were spending the money on," Edis told the jury of three men and nine women.
"They must have known, we say, where these stories came from, otherwise they would never have got into the paper."
Charges of conspiring to hack phones have been brought against Brooks, Coulson and Kuttner as well as former News of the World head of news Ian Edmondson.
But Edis stressed the case was about more than just phone hacking, noting that Brooks, Coulson and the News of the World's royals editor Clive Goodman are also accused of bribing public officials for information.
In one instance, Edis alleged that Brooks authorised payments worth STG40,000 ($A68,120) to a "highly placed" official at the defence ministry while she was editor of The Sun.
Coulson, meanwhile, is accused of conspiring with Goodman to pay a Buckingham Palace policeman to obtain copies of royal phone directories in a bid to access information on members of Queen Elizabeth II's family.
The flame-haired Brooks rose from a secretary to become chief executive of Murdoch's British newspaper wing News International, which was rebranded News UK after the scandal.
But she quit shortly after the paper was shut down in July 2011, after it emerged that the News of the World had hacked the phone of Milly Dowler, a missing teenage girl who was later found murdered.
Brooks is accused of trying to hide evidence from the police investigating hacking, along with her husband, racehorse trainer Charlie Brooks, her secretary Cheryl Carter and News International security chief Mark Hanna.