It may be almost 400 years since Guy Fawkes and his band of merry men became the most famous traitors in English history, but 5 November continues to be associated with gunpowder, treason and plotting.This year in particular the associations seemed particularly apt, as just days before, Defence Secretary Geoff Hoon had warned British Muslims who may be tempted to take up arms for the Taliban in Afghanistan that they face death if they join the war, and jail if they return to Britain.Tory MP Ann Widdecombe joined in the debate, saying in Parliament: 'If these Muslims come back to this country, they shouldn't imagine that they can just enjoy the democratic freedoms and rights of a free society when they have actively fought against it.'And across the corridor in the Lords, Tory peer Lord Tebbit has tabled a question asking 'whether it is a treasonable act for British subjects to take up arms against the forces of the global alliance against terrorism in general, or the Anglo-American forces in particular'.The concept behind treason -- meaning in its simplest form 'disloyalty' -- is that a citizen owes a duty of allegiance to his or her country in return for receiving the protection of the head of state.High treason is the act committed when that duty of allegiance is broken, for example, by fighting for an opposing country's armed forces.So are treason trials a realistic possibility, and will Guy Fawkes be joined in 400 years' time by effigies of British Taliban fighters?The simple answer is probably no.

To say that the original treason laws, contained in the High Treason Act of 1351, are not widely used is something of an understatement -- they have not even been included in the legal textbook Blackstone's Criminal Practice for a decade, and it is highly unlikely that many lawyers have studied the Act even as students.The original Act was specific in detailing treasonable offences, from counterfeiting coins to carnal knowledge of the wife of the heir to the throne.However, the most notorious crime contained in the 1351 Act -- when 'a man doth imagine the death of our King', or more aptly 'levy war against the King' -- is the most relevant to today's situation, and the legislation most likely to be quoted in court.However, there is a problem.

'Charges of treason, under the law that we have today, can only be brought when a state of war has been declared, or in the case of "actual hostilities" against the country,' says Joe Jacob, an expert on constitutional law at the London School of Economics.

'This explains why spies such as Anthony Blunt in the Cold War were never prosecuted for treason.'This also explains why the last person in the country to be tried for treason was William Joyce, popularly known as 'Lord Haw Haw', who was executed in 1945 for broadcasting Nazi propaganda to British audiences du ring the Second World War.Although Joyce was American born, the fact that he held a British passport -- albeit under an alias -- was enough for the prosecution to claim his allegiance to the Crown, and enough to see him climb the gallows.However, whether the current 'war against terrorism' falls into the 'actual hostilities' category, is very much a moot point, and Mr Jacob is dismissive of the current talk of treason.'It's outrageous, and just a load of hype,' he says.

'If a person commits murder, prosecute them for murder.

If they fight against this country, I have no problem with the state taking away their passport.

But treason laws do not apply in this situation, and playing fast and loose with the meaning of words for a cheap headline is wrong.'He also points out that talk of treason never came up in the context of Irish republicans who killed British soldiers in Northern Ireland during the troubles.'They were also technically British nationals fighting against the Crown's forces, and yet treason was never an issue,' he says.

The different treatments of British Muslims and Irish republicans, according to Mr Jacob, is 'deeply offensive', and moreover 'essentially racist'.Malcolm Fowler, the former chairman of the Law Society's criminal law committee, is equally unimpressed with the current talk of treason.

'Treason is a sensational peg on which to hang what are essentially normal crimes,' he says.'We have perfectly substantive and good laws that can be applied to these situations, and we should use these sensible and scientific laws to prosecute for crimes rather than go for the headline-grabbing, big-bang approach.'He acknowledges that 'treason may sound exciting and glamorous', but the reality is different.

'Treason is a very impractical law which is very difficult to prove,' he says.

'Taking this approach will mean that cases will founder because of a serious evidence shortfall, and these people will find themselves made martyrs, with their criminal acts suddenly elevated by the law to something sensational, attractive and dangerous.'There is certainly a general air of unease about the idea of treason.

Javaid Rehman, a lecturer in constitutional law at Leeds University, says the current debate is an interesting one.'From an ethical point of view, it is a fascinating conundrum -- it's a case where religion seems to be in direct conflict with constitutional and legal issues,' he says, describing the opinion of those fundamentalists encouraging young British Muslims to fight against the alliance.Even if young British Muslims do become enthused with fundamentalist fervour, they will not face the same penalty as Lord Haw Haw or the other three British men hanged for treachery in the aftermath of the Second World War.

During the last Parliamentary debate on treason in 1998, the death penalty was abolished.However, had the current situation come to pass a few hundred years ago the story would be a very different one.

'Henry VIII tightened up the treason laws considerably during his reign,' according to Mary Sokol, a solicitor and lecturer in law at Sussex University.

'He knew that his divorce from Catherine of Aragon and subsequent remarriage was controversial and deeply unpopular with many people, and so he made it a treasonable offence to criticise his marriage.'And simple executiion was not enough for this offence.

The punishment was to be hung, drawn and quartered.However, treason prosecutions did not end with the Tudor era.

'The heyday of treason prosecutions was in the 18th and 19th centuries,' says Dr Sokol.

'After the French revolution in 1789, the English authorities clamped down on people they saw as dissidents, members of "correspondence groups" which read and distributed pamphlets the authorities viewed as treacherous.'It was in this era of dissent that the Treason Felony Act of 1848 was introduced, making it a treasonable offence even to call for the establishment of a republic.The Act was unsuccessfully challenged in court by the Guardian newspaper earlier this year, which claimed that it fell foul of the Human Rights Act's guarantee of free expression.The fact that a little used piece of treason legislation was triumphant in court over the might of the modern day Human Rights Act seems neatly to sum up the issue.Judges, although loath to implement outdated treason legislation, are equally loath to put it away.

The same principles apply to the case of British Taliban fighters -- as a practical law, treason is all but useless, but as a legal, historical and deterring precedent, it is alive and kicking.