Those who post offensive messages on Twitter or Facebook are less likely to face criminal charges, under new guidelines set out by Director of Public Prosecutions Keir Starmer QC.
But the question of whether the country needs new laws to deal with offensive posts on social media is a question for Parliament, Starmer said.
Criminal prosecutions against people posting offensive online messages have controversially mushroomed in the past 18 months.
New guidelines are needed because of the potential for a "chilling effect on free speech" as thousands of people could be accused of being criminals every month, Starmer said.
Those who post offensive messages on Twitter or Facebook are less likely to face criminal charges
In a blog for The Huffington Post UK Starmer writes the guidelines draw a "clear distinction between those cases that constitute a credible threat of violence, stalking, harassment or a breach of a court order - clearly requiring robust prosecution in the public interest - and those cases characterised as unpopular, or even very offensive comments, which often will not."
The May 2010 conviction of Paul Chambers for joking on Twitter about blowing up Robin Hood Airport in South Yorkshire is one of most well-known cases in this area. His conviction for sending a "menacing" tweet drew widespread condemnation and was eventually quashed on appeal in the High Court in July.
Starmer now admits that the Crown Prosecution Service (CPS) made the wrong "judgment call" to prosecute the 28-year-old and included his solicitor in discussions over the law.
Now Starmer has set out new interim CPS guidelines designed to raise the threshold against which people should be prosecuted.
"In most cases, once you have put the (new) safeguards in place then a prosecution is unlikely to be the appropriate response.
To that extent, therefore, it is to make it less likely that these cases will be prosecuted," Starmer said.
The guidelines are intended to strike the right balance between freedom of expression and upholding criminal law, he said.
Now, social media messages which amount to credible threats of violence; a targeted campaign of harassment; or which breach court orders will be prosecuted robustly.
An example of this is the nine people each ordered to pay the woman raped by footballer Ched Evans £624 for naming her on Twitter or Facebook.
Her naming breached a court order prohibiting the identification of victims of sexual offences. Any similar cases would still be prosecuted robustly.
Aggressive "trolling" would also probably fall under this banner as it could be specifically targeted and constitute harassment or stalking, Starmer said.
But potentially "grossly offensive" messages will now only be prosecuted if they cross a high threshold.
The news rules mean that people like Matthew Wood, who was jailed for 12 weeks earlier this year for posting abusive messages on Facebook about April Jones, or Liam Stacey, who was jailed for tweets about Fabrice Muamba as he collapsed on the football pitch, may not have been imprisoned.
The guidelines point out that context is important and the tone of social media messages is different to other communications.
People often make spontaneous jokes or engage in offensive banter and comments "intended for a few may reach millions".
For criminal charges to be brought, a message must now be shown to be more than offensive, shocking or disturbing; more than satirical, iconoclastic or rude; and more than the expression of an unpopular or unfashionable opinion, the guidelines state.
Also if a message is swiftly deleted, blocked by service providers or websites or shown not to be intended for a wider audience, a prosecution is unlikely.
The message must be "obviously" beyond what is rightly considered tolerable or acceptable in a diverse society which upholds and respects freedom of expression.
Any prosecution must be in the public interest and therefore "necessary and proportionate".
But prosecutors must also weigh whether vulnerable victims may be more affected by offensive tweets than others and consider this in any decision to bring charges.
"In summary, there is a clear distinction between four types of case: the first three to be robustly prosecuted, the fourth (offensive messages) to be treated very differently," Starmer said.
"The fourth one is probably there where the more difficult decisions have been in recent months and certainly where there's been a growth in decisions. There we've put in a double safeguard: high threshold and unlikely to be in the public interest.
"It doesn't mean no cases but it certainly puts in that double safeguard before a case is brought."
The guidelines also state that children (under-18s) will rarely face criminal charges for offensive tweets or Facebook statuses, for example.
While intended for the CPS to make a decision whether to charge someone or not, the guidelines are also designed to offer early advice to police.
Chief Constable Andy Trotter, of the Association of Chief Police Officers, said: "(The guidance) takes a common sense approach and will help support consistency from prosecutors and police."
Javed Khan, chief executive of charity Victim Support, said: "This distinction between communications which constitute a credible threat and those which may merely cause offence is sorely needed.
"In particular, we welcome the guideline which makes a prosecution more likely if a victim is specifically targeted and this has a significant impact on them."
The interim guidelines take effect immediately and are now subject to a consultation process.
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