Jurors in Court 12 of the Old Bailey will have to determine three key issues about phone hacking at the News of the World: how much was there, when - and who knew?, the judge said today.

Beginning his three-day summing up in the phone hacking trial, Mr Justice John Saunders said the jury should disregard all extraneous matters when deciding whether the seven defendants were guilty or not guilty.

Addressing the eight woman and three men directly, Mr Justice Saunders said they should not feel sorry for the defendants, even though they may have had difficulties as a result of the allegations against them.

Andy Coulson, for instance, the judge said, had had a "dramatic fall" from his high-profile life, while Rebekah Brooks had received many hurtful and harsh comments in the media and elsewhere.

Mr Justice Saunders said: "Do not let your judgement be affected because some of them enjoyed a lifestyle like you or I can only dream about."

They are friends of stars who most of us only get to watch on the cinema or the football pitch. But do not envy their success, or be dazzled by it."

The judge continued: "Everyone in this country gets the same fair trial as everybody else."

He said the jury should think because of the humour sometimes displayed by the lawyers and the judge himself that the case or the charges were not serious, because they were."

It is simply that without humour the seven months would have been even more intolerable than we found them," the judge said.

He directed the jury that they could take into account the silence of five of the defendants when interviewed by the police they also had to weight up the fact that they were following the advice of their lawyers - which had not been disclosed to the court.

While some of the defendant's factual errors - such as Rebekah Brooks's PA Cheryl Carter telling he police her boss was away on a fitness "boot camp" at the time some boxes were removed from News International's archive - could be entirely innocent, it was also the case that sometimes defendants lied to protect themselves, he said.

Turning to phone hacking, the judge said there was no doubt that the privacy of individuals had been violated by the News of the World's practice of phone hacking. He mentioned two individuals whose messages had been eavesdropped for no good reason: Hannah Pawlby, advisor to Home Secretary Charles Clarke - whom the paper wrongly suspected was having an affair with the Labour politician - and Laura Rooney, who had been hacked only because she shared a surname with a famous footballer.

Mr Justice Saunders said: "Everyone is agreed that phone hacking went on at the News of the World: the issues are how much, when, and who knew about it."

His summing up continues. All defendants deny the charges.