Treason is a word that inspires dread like no other. Having echoed down the ages, but lain dormant for 60 years, the crime of high treason has resurfaced in British public discourse. The question that the government’s legal officers are reportedly considering is: Could Islamist clerics who incite Muslims to commit acts of terrorism in Britain, or to fight against British troops in Iraq and Afghanistan, be charged with treason?

Both the Conservative and Liberal opposition parties have dismissed the idea as a typical Tony Blair stunt, designed to sound tough but never intended seriously. The press has concurred that the prime minister is merely bluffing. On Tuesday Lord Chancellor Falconer beat a retreat, suggesting that lesser charges, such as incitement to murder, would do the same job of deterrence, without the gothic connotations of treason.

I am not so sure. Where Islamist terrorism is concerned, Mr. Blair does not usually do things by halves. Whether the statutes on treason, the most important of which goes back to 1351, are still practical today is a legal question on which very few lawyers are experts, though this is not the first time the issue has been aired. Four years ago, there was a discussion about whether British Muslims who joined the Taliban were guilty of treason.

What, though, constitutes high treason, for which the death penalty was formally abolished only when the European Convention on Human Rights was incorporated into British law seven years ago? “High” treason can only be committed against the sovereign; “petty” treason against others. The statute of 1351 states that high treason is committed “if a man do levy war against the king in his realm, or be adherent to the king’s enemies in his realm, giving to them aid and comfort in the realm or elsewhere.” Does this apply to the Islamists?

For guidance, I consulted the Lord Chief Justice in the early 17th century, Sir Edward Coke, whose “Institutes of the Laws of England” remains one of the sources from which flows the common-law tradition that England shares with America. It is from this work that these immortal words originate, justifying a man’s right to defend himself against intruders without fear of prosecution: “For a man’s house is his castle.”

Coke, by the way, was a lawyer whose avarice would gladden the hearts of any New York attorney today. He was reputed to have made $180,000 (perhaps $100 million now) in a single year, according to Aubrey’s “Brief Lives,” and when told that his sons would spend his fortune faster than he could earn it, replied: “They cannot take more delight in the spending of it than I did in the getting of it.”

But Coke was also a thorn in the side of the Stuart monarchy. He helped Parliament to stand up to Charles I with the Petition of Right in 1628, when he defiantly declared: “Magna Carta is such a fellow, that he will have no sovereign.”

Coke was well aware that treason laws can be used by tyrants to crush the natural liberties of man, and in his “Institutes” he discusses whether “bare words or sayings should be high treason.” Coke concludes, “the wisdom of the makers of this law would not make words only to be treason, seeing such variety amongst the witnesses are about the same [sic], as few of them agree together.” Words inciting men to levy war against the sovereign are treasonable (and hence capital offenses) only if they are “set down in writing by the delinquent himself,” for “this is a sufficient overt act within this statute.”

All this, though couched in Shakespearean prose, seems highly relevant to the present situation in England. For a charge of treason to be brought against the Islamist clerics, it is not sufficient to produce as evidence secretly recorded tapes, quoting – for example – one of the most notorious demagogues, Sheikh Omar Bakri Mohammed, privately praising the London suicide bombers of July 7 as “the fabulous four.”

But Mr. Bakri Mohammed has written and said quite enough on the record – on television, on his Web site, and in his books or public lectures – to give the authorities enough evidence to charge him with high treason. He praised the September 11, 2001, terrorists as “magnificent,” called on terrorists to “raise the banner of jihad inside the U.K.,” incited Muslims to fight British and American troops abroad, and acted as a recruiting sergeant for terrorism on campuses and at mosques. No wonder that, when he read that he might be charged with treason, he fled to Lebanon. Even if the talk of treason accomplishes nothing more than to frighten evil men like him, it has served a useful purpose.

The last man to be charged with treason in England was an American. He was also a Nazi. William Joyce, infamous during World War II as the broadcaster “Lord Haw-Haw,” was captured, tried, and executed despite the fact that he was born in America to an Irish-American father. The case turned on whether the British passport that Joyce held at the time he began broadcasting from Berlin (“Germany calling” was his motto) was valid, even though Joyce had obtained it fraudulently. The historian A.J.P. Taylor wrote that Joyce was hanged for making a false statement on his passport, the penalty for which was a $3.50 fine.

At the time, Joyce was probably the most hated man in England and his execution was popular, but the legal profession has had a bad conscience about it ever since. That is one reason why the present discussion of treason may well remain academic. The other reason, I suspect, is that to reintroduce treason trials would offend the liberal consensus; to do so against Muslims would outrage it. What a pity that the state’s first duty – to protect all its citizens – is likely to yield to the fear of offending Muslim clergy, who seem to have difficulty grasping why those who give aid and comfort to our enemies are indeed traitors.