By Jon Silverman
Legal affairs analyst
There are a number of offences with which protesters against the publication of anti-Muslim cartoons in London could be charged.
All decisions to prosecute require credible evidence
The brandishing of placards calling for others to be killed might be seen as incitement, which is a common law offence.
The prosecution does not have to prove that the act in question had been committed. Nor that the defendant had a named victim in mind.
Incitement to commit a serious act of violence, including murder, is more likely to be charged under the Offences Against the Person Act, 1861.
Section 4 makes it unlawful to "solicit, encourage, persuade or endeavour to persuade" a person to kill another anywhere in the world.
The maximum penalty is life imprisonment.
Another possible route to a prosecution is the Public Order Act 1986. This makes it unlawful to use " threatening, abusive or insulting words or behaviour".
In 2005, the owner-editor of a freesheet in north-east Scotland was charged under section 19 of the act for publishing an editorial attacking a plan to site a refugee centre in the area. The charge concerned the language he had used.
Since 1998, there has been a racially aggravated form of this offence, for which the maximum penalty is seven years imprisonment.
All decisions to prosecute require credible evidence and the application of a public interest test.
In other words, would the arrest and charging of Muslim protesters be a desirable course at a time when the government is trying to dampen down tension over the cartoons?
That will be a matter for the Director of Public Prosecutions to decide, having considered evidence gathered by the police.
It has been suggested that because the police chose not to make arrests at the demonstration itself, their investigating task will be harder.
Arrests often take place after a demonstration ends
But that is a misunderstanding of established police tactics at sensitive public order events.
Public safety is put before arrests and some officers are deployed at an event purely as intelligence gatherers.
Information they collect will be considered by the Met's public order crime unit.
It is not unusual for arrests to take place after the demonstration and for charges to be laid.
As the law stands, a protester dressed as a suicide bomber is likely to escape prosecution for that behaviour alone.
Mindful of the effect of such acts on the impressionable, the government wants to introduce an offence of indirect incitement of terrorist acts.
The vehemence of the anti-cartoons protests might have made the task of persuading its critics a little easier.