Lord chief justice raises concerns at the ease with which a juror can discover information about a trial

The integrity of the jury system is under challenge from temptations to trawl the internet for information about defendants, the lord chief justice will warn.

In the wake of a series of prosecutions of jurors who went online, Lord Judge has called for greater awareness about the technological dangers threatening the justice system.

Writing in the court of appeal's annual review, the lord chief justice said he was concerned at the ease with which a juror could discover information.

"I am also concerned that the use of technology enables those who are not members of the jury to communicate. In the context of current technology, we must be astute to preserve the integrity of jury trial and the jury system," he said.

In three separate appeals last year, convictions were found to be unsafe in the light of jury irregularities; re-trials were ordered in two of those cases.

In June, Joanne Fraill, 40, a juror in a Manchester case, was sentenced to eight months in jail for contempt of court after using Facebook to exchange messages with Jamie Sewart, 34, a defendant already acquitted in a multimillion-pound drug trial.

Fraill, from Blackley, Manchester, also admitted conducting an internet search into Sewart's boyfriend, Gary Knox, a co-defendant, while the jury was still deliberating.

Last month the high court gave permission for contempt proceedings to be brought against a juror whose internet research led to a criminal trial being aborted.

Theodora Dallas, a university lecturer, was hearing a grievous bodily harm case at Luton crown court in July when she looked up information about a defendant including a previous conviction.

"Next day, when the jury retired, she informed other members of the jury," the high court was told. "Her conduct was reported to the court and the judge discharged Dallas and the remaining jurors.

"This kind of internet research does constitute a contempt of court in that it creates serious prejudice to the administration of justice. That is the inevitable consequence."

The lord chief justice is due to publish his findings before Christmas following a consultation on the use of Twitter and text-messages in court. Reporters have to seek permission from a judge in order to send live tweets from the hearing.

Speaking earlier this week, he warned that jurors resorting to the internet may come across false information about individuals or uncover allegations that defendants had no chance to challenge.

He said: "If you introduce ... the entitlement of any juror to look up any piece of information he or she wishes, you end up with a trial based on the evidence called which the defendant and everybody else has had a chance to deal with, and whatever members of the jury have dug up for themselves.

"So when they retire, they will not be deciding the case on the basis of the evidence they have heard, having listened to both sides; they will be deciding the case on the basis of what they have heard, having listened to both sides, and all the other material which is completely extraneous, which may not be common to them all anyway. That is not our jury system."

The annual review of the criminal division of the court of appeal recorded a 2% decrease in the number of applications against sentences and conviction compared with 2009-10 (6,972 against 7,133).

Meanwhile the Magistrates Association has welcomed government suggestions that magistrates might be able to hand down sentences in cases where someone is charged and immediately admits guilt in a police station.

John Fassenfelt, its chairman, said: "We have been raising concerns about the misuse and abuse of out of court disposals [cautions and warnings given by the police] for the past three years and we are delighted that the government has acted."