Section five of the Public Order Act has a corrosive effect on free speech ? it's time to roll back the culture of offence

Sometimes you have to feel sorry for the police. Beyond already dealing with a raft of ill-considered laws, politicians also want them to act against "insulting" behaviour. Section five of the Public Order Act is so broad that almost any protester on any subject can be arrested and fined for harassment, causing "alarm or distress".

It's not merely theoretical; many ludicrous cases have been prosecuted. The police arrested a student who held up a sign stating Scientology was a cult ? surely a matter of opinion? Kyle Little, a 16-year-old from Newcastle, was fined ?50 with ?150 costs for saying "woof" to a labrador dog in front of police officers. Eventually the magistrates' decision was overturned by a crown court. The very arbitrary nature of deciding what is insulting gives the police a power they can misuse. After a night out with friends, Sam Brown asked a police officer: "Excuse me, do you realise your horse is gay?" Police took Brown to court after he refused to pay an ?80 fine. The CPS eventually dropped the case.

Criminalising "insult" has a detrimental effect on freedom of expression. The term is so broad that it creates legal inconsistencies. There is legal authority that defacing the American flag is a non-insulting form of protest but burning a poppy is criminally insulting. It makes little sense.

These powers are widely used during protests. Protest is often directed at an unsympathetic audience and will often directly cause offence. Oil companies may feel insulted by accusations of having blood on their hands, but there is a clear public interest in having opinions on the behaviour of the powerful heard.

Lord Justice Sedley said in Redmond-Bate v DPP: "Free speech includes not only the inoffensive but the irritating, the contentious, the eccentric, the heretical, the unwelcome and the provocative provided it does not tend to provoke violence. Freedom only to speak inoffensively is not worth having."

Yet, the inclusion of "insulting" in the Public Order Act means there is no clear jurisprudence between the offensive speech protected by Sedley and insult as criminalised by the act. Unfortunately most of these cases will go nowhere near learned judges, and the majority of these fines won't be challenged by a public that has never been informed of its rights. Very few of these cases get beyond a magistrates court, and divisional courts, where some of these fines have been quashed, are often loth to intervene.

When asked to determine the meaning of the word insulting under the previous form of the act, the House of Lords held in Brutus v Cozens that "parliament has given no indication that the word is to be given any unusual meaning. Insulting means insulting and nothing else".

This law, combined with our culture of offence, means there is the expectation that opinions deemed offensive should be criminalised. Our tolerance of the harmless eccentric has waned. The British no longer raise an eyebrow at fringe opinions, but demand the full force of the law. One example is Harry Hammond, a 69-year-old evangelist street preacher. Hammond believed homosexuality was a sin and wanted everyone to know this. So he stood in the streets of Brighton proselytising against homosexuality with a sign proclaiming the catchy slogan: "Jesus Gives Peace, Jesus is Alive, Stop Immorality, Stop Homosexuality, Stop Lesbianism, Jesus is Lord."

Instead of ignoring an old bigoted man, a crowd gathered. At one point he fell to the ground in a tussle over his placard, and soil and water were thrown over him. While Hammond was charged under section five, no one in the crowd was charged for assaulting him. He was fined ?300 by a magistrate and ordered to pay costs of ?395. The court also ordered the forfeiture of his sign. He died shortly after his conviction. Gay rights activist Peter Tatchell described Hammond's prosecution as "an outrageous assault on civil liberties".

While it's easy to see how Hammond's behaviour could rile a crowd, the danger with policing offence is that it's highly subjective. Perhaps only a generation ago, when there was very little tolerance towards homosexuality, a gay pride march could have been prosecuted for insulting Christians like Hammond.

Luckily, liberty has friends in parliament. Conservative MP Dominic Raab discovered that section five was used 18,249 times in 2009. Less than one in six of these offences had a religious or racial element, the majority were for the non-specified crime of insult. Following pressure from the Liberal Democrats, the Home Office consulted on this issue. My organisation, Index on Censorship, has been lobbying hard for ministers to roll back the culture of offence which has a corrosive effect on free speech. Removing insult from section five would be a good start.

Finding the correct balance between public order and legitimate protest isn't always easy. But asking the police to patrol offence has undermined public trust in them. Rightly so, for it is not the job of local bobbies or magistrates to protect citizens from insult. Christian preachers or mouthy anarchists may irritate, but in an open, free society, robust opinion will insult you: perhaps we all just need to get used to it.