The attempt to obtain an international arrest warrant for deputy Israeli prime minister Ehud Barak is the latest development in what lawyers describe as a rapidly growing area of law – "universal jurisdiction".
Under this principle, the most abhorrent crimes – such as genocide, torture and war crimes – can be prosecuted in the national courts of countries other than where they were committed. Customary international law and treaties such as the torture convention now place obligations on states to ensure that alleged perpetrators of these crimes are brought to justice, even it means trying them in their own courts.
The UK has not been as active as other European countries in implementing universal jurisdiction. In 2001 Belgium convicted four Rwandans for genocide committed in Rwanda, while Spain has prosecuted numerous human rights crimes committed abroad, particularly in South America.
However, the 1999 House of Lords judgment in the case of General Augusto Pinochet marked a major turning point for universal jurisdiction, eroding for the first time the principle that a former head of state could not be subject to trial in the courts of another country.
Experts say that since the Pinochet case, officials fearful of prosecution for torture and other serious crimes have avoided travelling to European countries where prosecution has been made more likely. Yet many states still practise a doctrine of restricted immunity – distinguishing between officials who travel in respect of their governmental acts as opposed to for commercial or private reasons.
In the only previous case in which the prosecution of a senior Israeli officer was attempted in the UK, a warrant was issued in 2005 for the arrest of Major General Doron Almog for the alleged destruction of 59 houses in the Rafah refugee camp on 10 January 2002. Almog, who had flown to the UK in 2005 for social and charitable visits, escaped arrest after a tip-off led him to remain on board his plane on the Heathrow airstrip. Officers from the Metropolitan police anti-terrorist and war crimes unit did not board the plane to arrest him.
Sources say that Israeli officials who face possible arrest are now careful to arrange state visits before arriving in the UK, building a pre-emptive defence that their presence falls under the immunity of a serving official performing government acts. Lawyers for Barak are already arguing along these lines, as he prepares to meet the prime minister, Gordon Brown, and foreign minister, David Miliband, during his trip to the UK.
However lawyers acting for the Palestinians seeking the warrant argue that further developments to the law since the Pinochet case have diminished the defence of state immunity. The recent arrest warrant issued by the international criminal court for the serving president of Sudan, Omar al-Bashir, marked a turning point in international law as Bashir became the first serving head of state to be indicted by the court.
Current attempts to obtain a warrant for Barak's arrest build on that precedent, claiming that the rules of customary international law on immunity no longer apply in the exercise of jurisdiction over the most serious criminal acts. Nevertheless there is still a lively debate in the legal community about whether, even if warrants can be issued for serving government officials, states have a duty to implement them by arresting and surrendering individuals like Barak to the court.
If Barak were arrested during his visit to the UK, it would mark a new precedent both for the evolving law of universal jurisdiction, but also the willingness of the UK courts and enforcement agencies to implement it.
Afua Hirsch, the Guardian's legal affairs correspondent.