A case that will decide the legality of the police containment tactic of kettling is to be heard at the European court of human rights in Strasbourg this week.
The case, brought by Lois Austin, began in 2001 after she was detained along with 3,000 protesters for up to seven hours at Oxford Circus in London during May Day demonstrations.
Trapped alongside her were tourists and newspaper vendors who were not part of the protest but were refused permission to leave the cordoned area by the Metropolitan police.
“I am deeply concerned that this tactic will discourage the next generation of peaceful protesters to express their legitimate concerns.”
The 2001 incident was one of the first major uses of kettling, and came as a response to protests by anti-capitalists the year before that saw Parliament Square vandalised and a statue of Winston Churchill defaced and daubed with graffiti.
Kettling has since been used by a number of police forces, particularly in the last 12 months as a response to anti-austerity protests, and most prominently during student demonstrations last winter.
In April the high court ruled that thousands of protesters were illegally detained in a kettle at G20 protests in 2009.
In 2009 the House of Lords ruled that the 2001 Oxford Circus "crowd control measures" had been proportionate. Today, lawyers acting for Lois Austin will argue that the ruling was flawed on the basis that it allowed Lois Austin's liberty to be deprived.
They will say in Strasbourg that article five of the European convention on human rights is an absolute right, and police detention tactics may not be justified by outcomes on the day and must be specified in law.
Lois Austin said: "Since the House of Lords judgment, the police have increased their use of the tactic of kettling, with disastrous consequences for the right to peaceful protest and the safety of protesters.
"I am deeply concerned that this tactic will discourage the next generation of peaceful protesters to express their legitimate concerns."
Kat Craig, of Christian Khan solicitors, said: "The police have, wrongly, taken the House of Lords judgment as a carte blanche to kettle protesters even when they are exercising their legitimate rights to express their opposition to government policies.
"The judgment threatens other aspects of personal liberty which are highly prized in any democratic society, such as the right not to be interned. It is imperative that this decision is challenged and [that] the balance which has for decades been struck between personal liberty and the power of the state is restored."