How the volunteers could be prosecuted

The determination of some British Muslims to join the Taliban's fight against the nation of their birth has sparked calls in some quarters for them to be charged with treason.

The Treason Act 1351 makes it a criminal offence to give aid and comfort to the monarch's enemies - and although the death penalty was formally abolished for the offence just three years ago, the crime is still punishable with a life sentence.

But the Act is not effective, the Home Office says, in the current conflict because Britain is not at war in a traditional "State versus State" manner. However, Britons who join the fight with Osama bin Laden and the Taliban could still be prosecuted and jailed on their return if they train for acts of terrorism or kill anyone abroad.

Section 54 of the Terrorism Act 2000 makes it a criminal offence to instruct, train or receive training in the making or using of a firearm, explosive or chemical, biological or nuclear weapons.

One person has been charged under this section of the Act since 11 September after allegedly offering "Ultimate Jihad" training for Muslims seeking to take part in a holy war.

The biggest task facing police and prosecutors would be gathering evidence against someone who had allegedly entered Afghanistan to fight against the West. But sources say the simplest catch-all piece of legislation to use would be the Offences Against the Person Act 1998 which means a Briton who kills anyone abroad can be tried in the UK.