The recent G20 summit in London highlights some of the powers provided by the common law — and also the potential for controversy if they're used.
The crowd-control tactic the Metropolitan Police colloquially calls kettling attracted a bit of criticism. (If you haven't seen or heard it, this article in The Guardian is scoring highly on digg and Technorati, along with this one.)
I haven't seen a definitive explanation of kettling, but it seems essentially to be a huge cordon that contains a crowd in one location for up to several hours. Its legal foundation rests on common-law preventative powers for police to prevent breaches of the peace. (Kerry Stephens wrote a very comprehensive article on that topic a few years ago in The Bulletin.)
Despite the criticism of the technique, the English Court of Appeal said it is lawful, in Austin v Commissioner of Police of the Metropolis  QB 660;  2 WLR 415.
On 1 May 2001 around 3000 demonstrators tried to enter Oxford Circus.
Around 2.15 pm the police threw a cordon around Oxford Circus. No one was allowed to leave without police permission. By 6 pm only around 400 people had been so released. The Court of Appeal described the scene.
[7.] The disruption to shops, shoppers and traffic by the events on that day was enormous. It was a wet and chilly afternoon. Oxford Circus has a diameter of about 50 metres, all of which is taken up by roads, pavements, and the four entrances to the Underground. There is no free space for people to congregate. The physical conditions in Oxford Circus were for a short period quite acceptable but as time passed the conditions became increasingly unacceptable. In particular, in the absence of toilets, people had to relieve themselves in the street in public. This and other problems bore particularly hard on some of the women. Fortunately no-one was seriously hurt but some of those attending came very close to sustaining injury and some policemen were injured.The two appellant-plaintiffs, Ms Austin and Mr Saxby, asked to be released, but were refused. Ms Austin made speeches as part of the demonstration till around 3.30 pm. She then asked to leave so she could collect her 11-month-old baby from a child-minder.
Mr Saxby was simply caught up in the demonstration, doing something unspecified for his employer.
Their actions alleged the tort of false imprisonment, and deprivation of liberty contrary to Article 5 of the European Convention for the Protection of Human Rights and Fundamental Freedoms. (That provision is similar to s 21 of the Charter of Human Rights and Responsibilities Act 2006 (Vic).)
There was no doubt the appellants' restraint amounted to imprisonment. The question was if it was lawful or unlawful.
The police argued it was lawful under:
- breach of the peace powers
- the Public Order Act 1986
The Court of Appeal didn't consider the Public Order Act in much detail, because it wasn't relied on at the original trial. They did discuss breach of the peace and necessity in great detail. In this case, they considered the two were intertwined. The Court adopted these five principles:
[35.] ...At  the Court outlined the facts the police relied on to satisfy those requirements.(i) where a breach of the peace is taking place, or is reasonably thought to be imminent, before the police can take any steps which interfere with or curtail in any way the lawful exercise of rights by innocent third parties they must ensure that they have taken all other possible steps to ensure that the breach, or imminent breach, is obviated and that the rights of innocent third parties are protected;(ii) the taking of all other possible steps includes (where practicable), but is not limited to, ensuring that proper and advance preparations have been made to deal with such a breach, since failure to take such steps will render interference with the rights of innocent third parties unjustified or unjustifiable; but(iii) where (and only where) there is a reasonable belief that there are no other means whatsoever whereby a breach or imminent breach of the peace can be obviated, the lawful exercise by third parties of their rights may be curtailed by the police;(iv) this is a test of necessity which it is to be expected can only be justified in truly extreme and exceptional circumstances; and(v) the action taken must be both reasonably necessary and proportionate.
The Court considered that the appellants were not about to commit a breach of the peace:  & .
But despite that, their 'containment' was lawful, under the doctrine of necessity, to prevent the risk of violence, injury to police and the public, and crime, they referred to in .
It was left to the discretion of individual officers to decide if people in the cordon obviously had nothing to do with the demonstration and to decide to release them. In the circumstances, there was no other alternative release policy open. (If the plaintiffs could show an individual officer was unreasonable in refusing to release them, that would have defeated the claim of necessity.)
Under Article 5 of the European Convention for the Protection of Human Rights and Fundamental Freedoms, the Court held the 'kettling' was interference with liberty of movement, not deprivation of liberty.
That meant the appellants were unsuccessful.
On my reading of Austin, the Court was operating right at the edge of its comfort zone, and not particularly happy about condoning the effective imprisonment of people in a small part of the city for up to 7 hours. But it was prepared to accept that extreme and exceptional circumstances might justify infringement of individuals' rights.
It may be Austin's decision is revisited following the London G20 demonstrations...