Policemen have many statutory powers to arrest those acting unlawfully, but often they exercise only the same powers of arrest which any citizen has. They exercise the common law right to arrest another citizen who has been misbehaving sufficiently seriously. The case of Bibby v Chief Constable of Essex Police CA Times 24-Apr-2000, re-states clearly the rules which apply in such situations. It demonstrates just how careful anyone seeking to act in this way must be.

The case set down four clear tests:

1. Only a sufficiently real and present threat to the peace can justify depriving a citizen, not then acting unlawfully, of his liberty (see Foulkes v Chief Constable of Merseyside Police ([1998] 3 All ER 705))
2. The threat must come from the person who is to be arrested (Redmond-Bate v Director of Public Prosecutions Times July 28 1998)
3. The conduct must clearly interfere with the rights of others and its natural consequences must be 'not wholly unreasonable violence' from a third party (Redmond-Bates)
4. The conduct of the person to be arrested must be unreasonable (Nicol and Selvanayagam v Director of Public Prosecutions ((1996) 160 JP 155)

Most importantly, this relates to a situation where the behaviour of the parties is, at the time of the arrest, not itself unlawful, but the person arresting anticipates that, but for the arrest, a breach of the peace, along the lines described above, is likely to happen in the very near future.

As always, the ordinary citizen who tries to effect such an arrest is asking for trouble.