Lord Goldsmith, QC, the former Attorney-General, recently published a report — “Citizenship: Our Common Bond” — in which he recommends that the laws of treason should be redesigned. The idea is to make the citizen’s duty of allegiance to the country “more relevant to modern conditions”. That’s a very good idea. Few laws are in greater need of updating. Today’s main treason law is found in the Treason Act 1351. You wouldn’t want to get dental or medical treatment according to the principles of 1351, and ancient law can be just as inapt.

Under the 1351 Act, anyone is guilty if he “levies war against the Sovereign” or is “adherent to the Sovereign's enemies”. Also guilty is anyone who “compasses or imagines the death of the Sovereign”. Those words come from a 14th century language known as “Law French”. It’s bit ridiculous to have to apply them to situations today.

The phrases do cover attempting to do anything by which the sovereign's life may be endangered or conspiring to do that. Mind you, that isn’t an entirely fresh interpretation — it was given at the trial of Ambrose Rockwood in 1696. You’ll get the flavour of that case when you know that he was charged that “being moved and seduced by the instigation of the devil” he conspired to kill King William III.

It’s also treason to slay the Lord Chancellor, or to violate (which in this context means to have sex with) the Sovereign's eldest unmarried daughter or the wife of the Sovereign's eldest son and heir. A person convicted of treason can be sentenced to life imprisonment.

Although the death penalty for murder was abolished in 1965, it remained a lawful punishment for treason until it was ended by the Crime and Disorder Act 1998. Last year, at the inquest into the death of Diana, Princess of Wales, five men were named by lawyers for Mohamed Fayed as having been her lovers: James Hewitt, Will Carling (the former England Rugby captain), Oliver Hoare (an art dealer), James Gilby (a PR executive), and Barry Mannakee (a bodyguard). She was divorced from Charles in 1996 but if any sexual relations had occurred between Diana and her lovers before 1996, then not only would the lover have been committing treason, he’d have been liable to be executed.

There have, in modern times been some notorious treason cases. Sir Roger Casement is sometimes said to have been hanged by a comma. Casement was convicted in the First World War of conspiring with the Germans to further an Irish insurrection. His conviction depended on how part of the 1351 Treason Act is punctuated.

You can, of course, significantly change the sense of one set of words by punctuation. For example, “a woman, without her man, is nothing” can be changed to “a woman: without her, man is nothing”. In Casement’s case, a comma appeared in a key clause of some, but not all, early versions of the 1351 Act. Ultimately, the court decided the comma was there (the judges inspected an ancient copy using a magnifying glass) and it allowed the definition of a traitor to include someone whose treachery, like Casement’s, was committed outside the realm. He made his nefarious plans with others while he was abroad. Casement was hanged at Pentonville prison in 1916.

Another case was the prosecution of William Joyce (popularly know as “Lord Haw-Haw”). He was an American citizen who lived in various countries and gained a British passport after making a false representation. During the war, Joyce broadcast Nazi propaganda on the radio from Germany. In sinister tones, he urged the British public to surrender. He was captured by British forces, brought back to England and charged with treason. The charge said that while “owing allegiance to the Crown” he sided with the enemy. Was he under a duty of allegiance to the Crown as alleged? The jury and House of Lords said yes. He was hanged at Wandsworth prison in 1946.

Today, cases are extremely rare. In 1981, 17-year old Marcus Serjeant was convicted, under the Treason Act 1842, for discharging a gun near the sovereign. The shots were blanks. The charge was “presenting a pistol at the Queen”. He was sentenced to five years. The idea of using treason laws against citizens sympathetic to Al-Qaeda was considered in 2005 but rejected as impractical.

Before the crime of treason can be redefined, it’s necessary for the UK to determine how we shall define the relationship between the citizen and the state. You can’t define treachery unless you’ve first defined allegiance. What duties of allegiance do citizens owe to the state? The government is currently consulting on this through its paper The Route to Citizenship.

The new law of treason will be, like the old law, not something that turns up in a court case near you any time soon. But how it’s defined is vitally important because it rests on whatever duty we collectively agree as citizens to owe to the state. A sound modern law of treason wouldn’t be so narrowly focused on fiends caught in royal beds as on those set on subverting democracy and the democratic state.

Professor Gary Slapper is Director of the Centre for Law at The Open University

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