Facebook and Twitter users are to be warned not to prejudice criminal cases before trials begin.
In a historic move, the Government's chief legal adviser will in future issue previously unpublished advisory notes to help prevent social media users committing a contempt of court.
Attorney General Dominic Grieve QC said the advisories, which have previously been issued only to print and broadcast media outlets on a "not for publication" basis, are designed to make sure that fair trials take place.
The Attorney General said he has changed the policy to stop the public tripping over legal pitfalls by commenting on court cases in a potentially prejudicial manner.
Grieve said: "Blogs and social media sites like Twitter and Facebook mean that individuals can now reach thousands of people with a single tweet or post.
"This is an exciting prospect, but it can pose certain challenges to the criminal justice system.
"In days gone by, it was only the mainstream media that had the opportunity to bring information relating to a court case to such a large group of people that it could put a court case at risk.
"That is no longer the case and is why I have decided to publish the advisories that I have previously only issued to the media.
"This is not about telling people what they can or cannot talk about on social media - quite the opposite in fact, it's designed to help facilitate commentary in a lawful way.
"I hope that by making this information available to the public at large, we can help stop people from inadvertently breaking the law, and make sure that cases are tried on the evidence, not what people have found online.
"This change also brings more openness to Government's dealings with the media so that both sides can be accountable to the public for what they do and say."
The advisories will be published on the Attorney General's Office (AGO) section of the gov.uk website and also through the AGO's twitter feed - @AGO_UK.