I'm afraid you're not quite right there. I've checked with a reliable source (offspring and their partner, who are both coppers). The offence is much broader than that and there apparently is no need for the arrestee to be or likely to be violent. Indeed, the offence is exactly what it sounds like.
Wikipedia describes it well: "In England and Wales, constables (or citizens) are permitted to arrest a person to "prevent a further breach of the peace" which allows for the police or the public to arrest a person before a breach of the peace has occurred. This is permitted when it is reasonable to believe should the person remain, that they would continue with their course of conduct and that a Breach of the Peace would occur."
There's no requirement that the person themselves is likely to or even might be violent or destructive. In numerous cases, people are arrested in this manner, because their presence or behaviour is likely to cause other people to breach the peace. The classic example is rival football fans. When fans of the visiting team display their team's colours and chant their team's songs in front of the home team's fans, the police are well within their powers to instruct the visiting fans to cease and desist, and to arrest them if they fail to do so. The reason for the arrest is the likely behaviour of the (usually) more numerous home fans.
:angel: