What do Peter Tatchell and the Christian Institute have in common? Before you answer, this isn’t some deeply unfunny jibe from a Coalition colleague, but one of many unexpected alliances which have formed to oppose Section 5 of the Public Order Act 1986.

This rather insidious Section criminalises all those who use “threatening, abusive or insulting words or behaviour, or disorderly behaviour” within the hearing or sight of a person “likely to be caused harassment, alarm or distress”. It also applies to those who display “any writing, sign or other visible representation which is threatening, abusive or insulting”.

A rather wordy piece of legislation but, in sum, the offence does not depend on harassment, alarm or distress actually having been caused. A recent legal textbook stated that, when this law was first passed, it extended the criminal law into areas of “annoyance, disturbance, and inconvenience”.

This raises all sorts of very difficult issues – if I say something offensive, and someone hears it, would I have committed an offence if I neither intended them to hear it, nor intended to cause offence? In my view, this represents yet another piece of bad legislation, resulting in our fundamental rights being decided by unaccountable guidelines.

But the difficulties with the Public Order Act run much deeper than this; they run to the very heart of how we perceive freedom and rights in this country. The criminalisation of merely ‘insulting’ behaviour in Section 5 means that, theoretically, the use of any words or opinions with which the majority do not agree is an offence.

The right to free speech is one of our most basic freedoms. The tension between Section 5 and the Human Rights Act is already evident: in 2009 the cross-party Joint Committee on Human Rights said that the reference to ‘insulting’ should be deleted “so that it cannot be used inappropriately to suppress the right to free speech”.

This might come as a bit of a shock to many readers – after all, the Act was passed in 1986 and most of us would still say that UK citizens enjoys freedom of speech. But the effect of the Act has already been seen.

In a 2008 case City of London police charged a teenager under Section 5 for demonstrating outside the London Headquarters of the Church of Scientology with the word “cult” on a placard. The charges were dropped days later.

The Christian Institute cites a case of hotel owners charged following a religious discussion with a Muslim guest, while gay rights campaigners have themselves been prosecuted for criticising homophobic religious campaigns.

Few cases like these lead to successful prosecutions, but if the police can arrest you while you’re out protesting, merely for expressing your own opinions, then we are entering very dangerous territory.

That is why myself and fellow Lib Dems garnered cross-party support for an amendment to the Protection of Freedoms Bill to remove the use of the word ‘insulting’. After sustained pressure, the Government has launched a consultation to “assess the benefits of removing ‘insulting’ from section 5 of the Public Order Act 1986”.

The current law encroaches on the fundamental right to free speech, it is being used to prosecute those whom it was designed to protect and it is fundamentally illiberal. It is shameful that the previous Government took no steps to remedy this. We will not make the same mistake: the law should be changed as quickly as possible.