Twitter can be used in courts but users will need the judge's permission first and this could be refused in criminal trials, the country's top judge said today.
Lord Chief Justice Lord Judge said decisions over the use of the micro-blogging website would be made on a case-by-case basis depending on the risk of interference to the "proper administration of justice".
This risk would be at its highest in criminal trials where witnesses outside the courtroom could find out what is being said inside before being called to give evidence, he warned.
Lord Judge added that the use of Twitter in courts could also be limited to journalists, rather than any member of the public, to stop large numbers of mobile phones interfering with the court's sound recording equipment and to prevent other distractions.
His interim guidance on the use of the micro-blogging site and electronic devices in courts comes ahead of a consultation on the issue.
He said: "The judge has an overriding responsibility to ensure that proceedings are conducted consistently with the proper administration of justice, and so as to avoid any improper interference with its processes.
"There is no statutory prohibition on the use of live text-based communications in open court.
"But before such use is permitted, the court must be satisfied that its use does not pose a danger of interference to the proper administration of justice in the individual case.
"Subject to this consideration, the use of an unobtrusive, hand-held, virtually silent piece of modern equipment for the purposes of simultaneous reporting of proceedings to the outside world as they unfold in court is generally unlikely to interfere with the proper administration of justice."
He went on: "The normal, indeed almost invariable, rule has been that mobile phones must be turned off in court.
"An application, whether formally or informally made (for instance, by communicating a request to the judge through court staff) can be made by an individual in court to activate and use a mobile phone, small laptop or similar piece of equipment, solely in order to make live text-based communications of the proceedings.
"When considering, either on its own motion, or following a formal application or informal request, whether to permit live text-based communications, and if so by whom, the paramount question will be whether the application may interfere with the proper administration of justice.
"The most obvious purpose of permitting the use of live, text-based communications would be to enable the media to produce fair and accurate reports of the proceedings.
"Without being exhaustive, the danger to the administration of justice is likely to be at its most acute in the context of criminal trials - eg, where witnesses who are out of court may be informed of what has already happened in court."
The announcement that he would be giving the guidance was made last Thursday - hours after supporters of WikiLeaks founder Julian Assange were banned from posting updates from court while a High Court judge decided whether he should be granted bail.
Mr Justice Ouseley, who went on to give Mr Assange conditional bail that day, ruled at the start of the proceedings that supporters and journalists should not send Tweets to give a blow-by-blow account of what was happening.
At an earlier bail hearing, District Judge Howard Riddle had allowed Tweeting from City of Westminster Magistrates' Court, which some commentators proclaimed as a legal first.
He said journalists could send messages as long as they were discreet and did not interfere with the judicial process.