Fresh advice from director of public prosecutions applies to protests that turn violent or result in criminal damage

People who mask their faces to conceal their identity or carry anything that could be used as a weapon during protests should be pursued more vigorously by the law in the event of disorder, according to fresh guidance from the Crown Prosecution Service.

Telephone and computer records should also be checked to see if there is evidence of planning violent or illegal disturbances, the advice drawn up by the director of public prosecutions (DPP), Keir Starmer QC, states. Prosecutors are also being urged to work more closely with the police to examine social network sites.

The 13 page document, which will be circulated to CPS prosecutors on Tuesday, applies to public disorder cases such as demonstrations that turn violent or result in criminal damage rather than the more serious outbreaks of rioting experienced last summer.

The DPP's guidance is intended to strike a balance between the rights of peaceful protest and free speech, and preventing the breakdown of public order.

Prosecutors are encouraged to draw a distinction between those who organise or anticipate criminal offences and others who may have been caught up in illegal actions. It may not necessarily be in the pubic interest to bring charges against the latter group, the guidance says.

"It is ? essential that the evidence in public protest-related cases is carefully scrutinised, especially where those involved have covered or partially covered their faces and/or where arrests take place some time after the incident in question.

"Prosecutors should have particular regard to whether there is evidence that a person had come to the protest equipped with clothes or mask to prevent identification, items that could be considered body protection, or an item that can be used as a weapon, as it may indicate the person came in anticipation of disorder at the protest or there was an element of planning before the commission of the offence."

Other signs of planning may be stored online or in data records, the CPS advice says. "Prosecutors should consider whether there is evidence of telephone or computer records or social network activity that show that the suspect was closely involved in the commission of the offence.

"There may also be CCTV coverage or video footage from the police or videos made by protesters uploaded onto the internet that may provide evidence of a person's participation in an incident."

The advice has been issued following a series of appeal cases over what constitutes freedom of expression, under the European convention on human rights, in the context of public demonstrations.

Starmer told the Guardian: "The purpose of the guidance is to distinguish between those who want to be violent and disruptive and those who go with an essentially peaceful purpose but get caught up in things.

"There's a potential for a number of protests over the coming years that may be quite large ? If someone has brought along a weapon or means of concealing their identity that's likely to be evidence that they were anticipating trouble or disorder."

Postings on social networks can equally be indications of arranging violent confrontations, the DPP explained. The sit-ins in Fortnum & Mason during anti-City protests, he suggested, were an example of large number of demonstrators being caught up unintentionally in trouble. Some of the charges have since been dropped.

The guidance is aimed at striking the right balance between preserving free speech and preventing the break down of law and order, Starmer added.

"It seeks to balance the public's rightful expectation that offenders should face justice, with our legally enshrined, and age-old tradition, of peaceful protest.

"So criminals bent on disruption and disorder are warned they will not get an easy ride. My intention is that this guidance should ensure these difficult cases are dealt with proportionately and consistently."