//Yes, but "wilful obstruction of the highway" is a non-indictable offence (Section 137, Highways Act 1980) and therefore police do NOT have the power of arrest in relation to it.//
The idea of an “arrestable” offence has gone out the window, ‘Chico. The Serious Organised Crime & Police Act 2005 abolished the statutory concept of the “arrestable offence”. A police officer can arrest a person for anything if he has reasonable suspicion that he has been involved in a crime and that his arrest is necessary. In England & Wales (but not in Scotland) there is no offence of “Breach of the Peace.” An officer can arrest an individual to prevent a BotP, but the individual cannot be charged with it.
The problem is not really getting the idiots off the roads. The police have adequate powers to do that. The problem is what happens next. The charges which seem appropriate to this behaviour are, as ‘Chico mentions, “non-indictable”. In fact they are “summary only.” This means (assuming they are sentenced to the maximum, which is highly unlikely) the maximum sentence is six months and due to early release and Home Detention Curfew, that means just six weeks would be spent inside. There is certainly a case for refusing bail (on the basis that there is ample belief that further offences will be committed). But “custody time limits” (CTL) mean that the maximum a defendant can be remanded in custody is 56 days. It is most unlikely – especially at the moment – that the matters can be prepared and court time found to handle the large number of cases that are likely to arise from mass arrests at these incidents. Although there is provision for a court to extend that limit if they believe it is necessary in the interests of justice to do so, no court is going to extend a CTL of 56 days, when the absolute maximum the defendant would spend in custody if convicted is 42 days.
In short, the justice system is not geared up to preventing the chaos that these people are causing. The idea of using court orders to prevent repetition is probably the best there is, but it is limited in its use. Such orders have be served on individuals and they have to be specific in what they prohibit. Vague or wide reaching orders are likely to be successfully challenged.