The word "sedition" brings to mind mutiny, treason and treachery, preferably against a monarch. In the 1992 film Last of the Mohicans, for example, one character, Colonel Munro, expresses his anger at the suggestion of some colonials leaving a fort while it is being attacked by the French: "Anyone fomenting or advocating the leaving of Fort William Henry will be hung for sedition. Anyone actually caught leaving will be shot for desertion!".

The non-legal usage of the word, in both Spanish and English, reflects that history. Spain's dictionary of reference, the RAE, defines it as "a collective and violent uprising against authority, public order or military discipline; without being as serious as rebellion". The Oxford English Dictionary describes "Conduct or speech inciting people to rebel against the authority of a state or monarch".

So when the National High Court jailed two Catalan separatist leaders—Jordi Sánchez (ANC) and Jordi Cuixart (Òmnium Cultural)—last week for "sedition", or earlier when the Public Prosecutor announced the "sedition" accusations, the story quickly resonated around the world, in conflict-filled headlines: "Spanish court jails Catalan separatists pending sedition trial" (Politico), "Catalan police chief faces sedition investigation" (FT), "Catalans protest sedition case after Spain's top court rules independence vote was illegal" (LA Times), or "Spain Sees Signs of Catalan Police Sedition as Rebels Dig In" (Bloomberg).

The modern legal description in Spain's 1995 Criminal Code, however, contains no references to the 17th Century or to Fort William Henry. "Sedition" in modern Spanish law is a public order offence. The crime of "sedition" is described as forcefully or unlawfully preventing officers of the law from properly enforcing that law or from otherwise executing their duties, "in a public and tumultuous manner". Sentences range, on the low end, from four years in jail for ordinary participants to, on the high end, 15 years for organisers in positions of authority.

The crime of "rebellion" also exists in that modern Criminal Code, and that's where "declaring the independence of part of the national territory" or "substituting the government of the nation for another", among others, come in.

"Rebellion" carries a prison sentence of up to 30 years in jail for the leaders, depending on how serious it is considered to be. Spain's Director of Public Prosecutions, José Manuel Maza, has not ruled out such a charge for Carles Puigdemont, but he has not announced it yet, and "rebellion" is not what Cuixart and Sánchez—and Catalan Police chief Josep Lluis Trapero—are being investigated for.

That 1995 revision of the Spanish Criminal Code also got rid of the crime of "improper sedition", which included the non-violent, non-tumultuous declaration of independence.

In her ruling on October 17, National High Court judge Carmen Lamela was quite clear on the "seditious" nature of the actions carried out by Jordi Cuixart (Omnium Cultural) and Jordi Sánchez (ANC), but she was of course referring to "sedition" in its specific modern legal sense. In its accusation on September 22, the Public Prosecutor's Office described up to 40,000 people blocking Civil Guard agents acting as judicial police, and other officers of the court, inside the regional economy ministry building in central Barcelona for nearly 24 hours.

One female clerk of the court had to escape across the roof to the next-door theatre and leave mingled in with the crowd after a show. The others remained blocked inside until 7 a.m. the following morning. Outside, three Civil Guard SUV patrol vehicles, containing weapons, were trashed by the crowd. The judge and prosecutor describe how separatist organisations sent out calls for protestors to swarm the area outside the building, how the ANC set up a volunteer stand to organise the protest, and how Cuixart and Sánchez encouraged the mass of people.

Judge Lamela does describe related events that are more obviously separatist in nature in her remand decision—to explain the context and aims of the protestors that day, and over a period of several weeks—but specifies that those are not the events under investigation in the current case.

So how would those events of September 20—and not the more historical concept of treachery against a state—be investigated in other modern Western democracies? The Crown Prosecution Service declined to offer formal comment, but suggested The Spain Report speak to professors who specialise in policing and public order matters.

David Mead is Professor of UK Human Rights Law in the School of Law at the University of East Anglia. His research focuses on protest and public order, as well as British human rights law. Clifford Stott is a Professor of Social Psychology at Keele University who studies crowd behaviour, riots, hooliganism and public order, and who has advised the Home Office, the European Union, UEFA, the Association of Chief Police Officers and several British constabularies.

Both men agreed a range of offences would likely be considered in the UK, from the relatively minor "obstructing a police officer", or the catch-all "breach of the peace", through to "affray", "violent disorder" and "riot", contained in the Public Order Act 1986 and "false imprisonment", a common law offence.

The CPS describes false imprisonment as "a common law offence involving the unlawful and intentional or reckless detention of the victim. An act of false imprisonment may amount in itself to an assault".

Riot, as defined by the Public Order Act 1986, is described as: "twelve or more persons; present together; used or threatened unlawful violence (all charged must use); for a common purpose; and that the conduct of them (taken together); was such as to cause; a person of reasonable firmness; present at the scene; to fear for his personal safety".

"A person guilty of riot is liable on conviction on indictment to imprisonment for a term not exceeding ten years or a fine or both".

False imprisonment is punishable by a very long prison sentence or even a life sentence, depending on the seriousness of the circumstances.

"As a common law (i.e. not in an Act/statute)", said Professor Mead: "false imprisonment will carry a maximum life sentence - though the likely sentence under sentencing guidelines will be much, much less than that".

He said sedition as a crime had been abolished in the UK in 2009: "If it had still been around now, its constituent elements in broad terms are 'encouraging the violent overthrow of democratic institutions' taken from a case called Choudhury in 1991, where a group of Muslim leaders tried to have Salman Rushdie prosecuted for it, and for blasphemy. Their claim was unsuccessful".

Professor Stott said there were "a number of complex issues" surrounding the different concepts: "public order law is a relatively undefined way of the state exercising control [over individuals] […] all public order is like that".

He highlighted sentences awarded to two men in Cheshire in 2011 for inciting riots—which did not then took place—on Facebook. A judge in Chester sentenced them to four years in jail.

"They both used Facebook to organise and orchestrate serious disorder at a time when such incidents were taking place in other parts of the country", said the CPS in a statement at the time: "these posts caused significant panic and revulsion in local communities as rumours of anticipated violence spread".