The police have a duty to maintain public order and prevent any violence from occurring. In this scenario, the police have received information that a group of potentially violent individuals are heading towards the demonstration. As such, they may use their powers under the Public Order Act 1986 to prevent violence and disorder. Under section 12 of the Public Order Act 1986, a senior police officer may impose conditions on public processions if they believe that the procession may result in serious public disorder, serious damage to property or serious disruption to the life of the community. This includes conditions such as the time and route of the procession.

If the police believe that violence is imminent, they may use their powers under section 60 of The Criminal Justice and Public Order Act 1994 to stop and search individuals without reasonable suspicion. This power may only be used where the police believe that there is a risk of violence, and the use of the power is necessary to prevent it.

In the case of R v. Jones [2006] UKHL 16, it was held that the police may use their powers to prevent violence before it occurs, even if this means restricting the right to protest. However, any restrictions on the right to protest must be proportionate and necessary to prevent violence.