Former News of the World editor Andy Coulson, who later became Prime Minister David Cameron's media chief, denies conspiring to illegally access celebrities' voicemail messages in a scandal which forced Rupert Murdoch to shut the paper in 2011.
The trial heard on Thursday that Coulson had been having an affair with fellow defendant Rebekah Brooks, his predecessor as editor and a close Murdoch confidante, for much of the time the pair are accused of involvement in hacking.
Continuing to set out his case on Friday, prosecutor Andrew Edis said Coulson, as editor from 2003 until 2007, must have known his journalists were routinely hacking phones to glean stories for the tabloid, which prided itself on its celebrity scoops.
"Does he know about phone hacking? He says he doesn't. We say: 'Oh yes, he did'," Edis told the court.
The jury heard that in May 2006, the paper was seeking to run a story about television personality Calum Best, the son of late Manchester United football star George Best, according to media reports from the trial.
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In an email exchange with Ian Edmondson, the tabloid's former head of news who is also on trial, Coulson wrote: "Do his phone," the court was told, the reports said.
Edis told the jury of nine women and three men they would have to decide what that meant.
Prosecutors revealed Coulson's 1998-2004 affair with flame-haired Brooks on the grounds that it showed they "trusted each other" and would have shared details about hacking at the paper.
In a letter found on Brooks' computer, dated 2004, she wrote to him: "I tell you everything, I confide in you."
Brooks was editor from 2000 until 2003 when Coulson, her deputy, took over.
Having started out as a secretary at the News of the World, she went on to become chief executive of Murdoch's British newspaper operations.
Coulson meanwhile became David Cameron's chief spin doctor in 2007 but was forced to resign in 2011 over persistent claims that he knew more about hacking at the News of the World than he had admitted.
Prosecutors argue that Brooks, Coulson and the tabloid's managing editor Stuart Kuttner must have known about hacking because they were keeping a close eye on its budget, and obtaining hacked information was expensive.
Private investigator Glenn Mulcaire, who has previously been jailed for hacking, was paid STG100,000 ($A170,600) a year to work with an investigations team that routinely used hacking, prosecutors say.
Targets of the paper included actors Jude Law and Sienna Miller, former interior minister Charles Clarke and a former aide to Prince William and his brother Harry, Edis told the court.
On occasions, Edis said, the paper hit the wrong targets - such as when it hacked the phone of a hairdresser named Laura Rooney, falsely believing she was related to the England football star Wayne Rooney.
"She was not related to Wayne Rooney and has nothing to do with him," Edis said.
