A juror who "deliberately disobeyed" repeated instructions not to seek information on the internet about the case she was trying has been given a six-month jail term for contempt of court.

Lord Judge, the Lord Chief Justice, used the case of "highly intelligent" academic Theodora Dallas to send out a warning that the misuse of modern technology by jurors would almost inevitably land them in prison.

Attorney General Dominic Grieve, who prosecuted Dallas, 34, for contempt of court, said the case sent out an "important message".

Mr Grieve said: "It is central to the fairness of our trial process that only what is heard in court should determine the jury's verdict."

But concerns were raised by the Prison Reform Trust over the adequacy of the guidance given to jurors "and the effectiveness of the use of imprisonment as a deterrent to others".

Dallas, a Greek national who came to England at the age of 19, caused the trial of Barry Medlock at Luton Crown Court to be abandoned last July after she discovered on the internet that Medlock, who was accused of assault occasioning grievous bodily harm with intent, had been previously charged with rape - an offence of which he was acquitted.

Lord Judge said Dallas had struck the court as "a highly intelligent woman, extremely articulate in English" who had described being "overwhelmed by the honour" of being summoned for jury service. But her fellow jurors were "extremely disturbed" when she discussed the rape allegations.

Lord Judge, sitting with Lady Justice Hallett and Mr Justice Openshaw, said Dallas had denied contempt. However there was "no doubt" that she knew "perfectly well" that the trial judge had directed her and the other members of the jury "in unequivocal terms" that they should not seek information about the case from the internet.

There was also no doubt that she "appreciated that this was an order" and that she "deliberately disobeyed the order".

He rejected pleas from Charles Parry, appearing for Dallas, that she should be shown mercy and given a suspended jail sentence.