Keir Starmer is a busy man. Besides being pulled into the increasingly sordid Saville scandal (more on that another time), the Director of Public Prosecutions (DPP) finds himself in the midst of one of the most contentious debates in history of media law. 

It all revolves around the huge popularity of social networks and the potential for unfettered users to persistently harass or incite hatred. Facebook now has more than one billion users and there are more than 250 million tweets posted each day. In turn, there are more offensive comments about others being made than ever before. For this reason it is even more important to review legislation and the limits on freedom of speech in light of new technology.

In the UK alone, the number of social media-related harassment cases has risen from 2,347 in 2010 to 2,490 in 2011. And that number could rise sharply. Yesterday, Starmer addressed a gathering at London School of Economics (LSE), explaining that "if you retweet, you commit an offence under the Act." The legislation in question is Section 127 of the Communications Act 2003, which outlaws sending a tweet that is "grossly offensive or of an indecent, obscene or menacing character". According to the Act, a person can also be prosecuted if he or she "causes any such message or matter to be so sent". 

This has set alarm bells ringing in the ears of the Twitter community and libertarians nationwide, many of whom believe that the right to free speech should be absolute. In fact, Alex Macgillivray, the general counsel for Twitter, is known for describing the microblogging service as "the free-speech wing of the free speech party". For how much longer though… At the beginning of this year the micro-blogging service announced that it would now be able to selectively block tweets on a country-by-country basis, acknowledging that "different countries would have different ideas about the contours of freedom of expression".

So far, courts in the UK have erred on the side of caution, but that isn't to say that they have ruled with consistency. In 2010, Paul Chambers was arrested for tweeting: "Crap! Robin Hood airport is closed. You've got a week and a bit to get your shit together otherwise I'm blowing the airport sky high!" He was found guilty at Doncaster magistrates court, and went on to lose his first appeal and a High Court appeal, before a second High Court appeal finally saw his conviction quashed on July 27 2012. Chambers' tweet was retweeted thousands of times by sympathisers; based on Starmer's view at LSE today, those people would theoretically be liable for prosecution.

In March, Swansea student Liam Stacey was sentenced to 56 days in prison for racially offensive comments on Twitter about the seriously ill Bolton Wanderers footballer Fabrice Muamba. The judge described the comments as "vile and abhorrent" and added that "there is no alternative to an immediate prison sentence". The decision was welcomed by a mass of sympathisers, but it was not without its fierce critics, who claimed that Stacey was not guilty of a public order offence and that the sentence was highly excessive. Others point to regularly outspoken tweeters such as Frankie Boyle and wonder how he gets away with half the offensive things he says. Perhaps it's because he's a comedian; it's a joke so he doesn't mean it…

Last month the CPS decided not to take action against Daniel Thomas, a semi-professional footballer at Port Talbot Town FC, who posted homophobic messages on Twitter relating to the Olympic divers Tom Daley and Peter Waterfield. The Crown Prosecution Service (CPS) stressed the importance of the sender's intention and ruled that his actions, "however misguided", were intended to be humorous to family and friends, and not grossly offensive to the divers.

Earlier this month, 20-year-old Azhar Ahmed was sentenced to 240 hours of community service for a Facebook post saying, "all soldiers should die and go to hell" following the deaths of six British soldiers. Soon after, Matthew Woods, also 20, was jailed for 12 weeks after posting "sick jokes" about missing girl April Jones on Facebook.

Whether you are aggrieved by the curbing of free speech or alarmed by the number of people casually causing offence, one thing is clear: the situation is getting out of hand and the Communications Act, conceived at a time when few could imagine just how instantaneous the transition from private thoughts to mass communication would become, is not comprehensive and clear enough to address the myriad situations that arise.

Starmer's position is quite clear. On BBC's Newsnight a fortnight ago he acknowledged a person's "right to be offensive and insulting" as well as 'the chilling effect" that an amendment to legislation could have on free speech. But he wants guidelines to be drawn up that will help to clarify the situations where prosecution is justified. He has mooted two categories: where there is a "campaign or harassment or a general credible threat" and " where communications are merely offensive or grossly offensive". (The former would require a high threshold of criminality and the latter would not necessarily be ring-fenced from prosecution.)

Over the next few months the CPS will consult lawyers, academics and representatives from social media sites such as Twitter and Facebook – both of whom are keen to be very hands off, relying mainly on community policing – as well as leading sports bodies including the Football Association, the Rugby Football Union and the British Olympic Association. The results will be shared before Christmas.

Ultimately, the aim should be to preserve democracy, outlining how the law will be clearly and consistently applied when an individual oversteps the mark. That is the challenge for Starmer and his colleagues – which words or deeds would most of us consider to be grossly offensive? We have all seen how revolutionary an advancement the internet, more affordable technology and the creation of social networks have been in giving a voice to those who were once disregarded or, worse still, suppressed. Look at the legitimate battle against "The Great Firewall of China", the toppling of dictators in Egypt and Tunisia (not that I am disregarding the power of the human spirit) or one "anonymous cyber-dissident's" exposure of corruption in Saudi Arabia.

On the other hand, the internet is not a parallel universe where people can roam free, attack, threaten or defame others and not expect there to be consequences. The inhibition-loosening age of the internet and rapidly advanced remote communication have made many of us intemperate and uncivil. People don't think hard enough before they act: that comment on YouTube or under a news article; Tweet exchanges that quickly escalate.

You may not be seen but you are heard nonetheless, and you're not necessarily taken less seriously, as lawyer Keith Ashby recently claimed, just because you're not face to face. Social networks have amplified people's voices, sometimes for the good, other times less so. One person co-ordinates troops for a riot and mass looting; another organises a mass clean-up operation in their neighbourhood. For that reason those who misuse social networks must be held to account if they act with malice or embark on a campaign of abuse and incitement to violence.

It is not in anyone's best interests to have more prosecutions and a more litigious society in the UK. So let's combine efforts to avoid any more nasty incidents: responsibility for policing social networks should be shared between the community, the courts (where necessary) and above all, the service providers. Justice Secretary Ken Clarke, speaking in relation to a review of the Defamation Bill, has said that, "Website operators are in principle liable as publishers for everything that appears on their sites, even though the content is often determined by users." I would extend part of that responsibility to highly successful companies such as Facebook and Twitter, encouraging them to invest more in moderation and work more closely with government or police departments. The privilege of being able to voice your opinion to millions should be taken away from those who don't act respectfully towards their peers.

Meanwhile, this debate plays out across the world. In India this August, extremists in two rival communities provoked a full-scale sectarian conflict by using Twitter to spread rumours that each side is attacking the other, supporting the charges with falsified pictures of purported victims. Violence erupted in Assam where both communities are based, killing 80 people and displacing 300,000. The rumours on Twitter quickly followed, causing tens of thousands of people elsewhere in India to flee for fear of their lives. After a tense stand-off between Twitter and the government, the social network agreed to remove six troublesome sites but not the spoof accounts of those impersonating and ridiculing the prime minister.

I do hope that Starmer and his team take this opportunity to lead the way and formulate a just and pragmatic set of guidelines that others can adopt. Common sense should prevail, together with an inate sense of right and wrong. Chambers' airport outburst did not constitute a "credible and genuine threat" in my view, although perhaps he should have chosen his words more carefully, but the comments of Stacey, Ahmed and Woods were indefensible in their context.