A Westminster think-tank has called for the scrapping of a law which it claims is being used to constrain freedom of speech.

Civitas is calling for the abolition of Section 5 of the Public Order Act, which has been criticised by free-speech campaigners.

David Green, director of Civitas, said: "The freedom to speak our minds without fear or favour is an important part of the live and let live ethos that has typified this country for centuries.

"Throughout most of human history the suppression of unwelcome opinions has been normal, and open societies in which we try to conduct arguments without violence have been a great human achievement. Speech laws are an attempt to return to the primitive ways we have left behind."

The think-tank has published a book, Feel Free To Say It, which says Britain is sacrificing its commitment to freedom of speech to protect people from hearing views they do not like.

According to author Philip Johnston, a raft of laws from recent decades are having "a significant and deeply chilling effect" on speech in public.

He warned the law is being used to constrain opinions "because some people may not like them", and claimed the UK was in danger of "throwing away the freedom that makes all other liberties possible".

In January the Government said anyone caught making spurious insults in public should not be prosecuted. Home Secretary Theresa May said ministers planned to drop the word "insulting" from Section 5, which saw a number of spurious arrests and court cases.

One teenage boy was detained for holding a "Scientology is a dangerous cult placard", while a student was held after telling a police officer his horse was "gay".

In another case, a man was arrested for growling and barking at a pair of Labradors, and a cafe owner was warned by two police officers after he showed DVDs displaying texts from the New Testament.