The letter, initiated by the Canadian Bar Association and sent last week, accuses the US and Canadian governments of denying detainees a fair trial and of treating the rule of law as an “inconvenient afterthought”.

The letter states: “Few governmental operations in democratic countries have shown such a profound disrespect for the rule of law. Guantanamo Bay has come to signify injustice for some at the hands of the powerful.”

The letter particularly condemns the US Military Commissions Act of 2006 under which a person can be trialled by a military commission on the basis of their status as an alien. The Act also allows a military commission to consider coerced statements and for defence counsel to be denied access to evidence on the basis of “national security”. According to the letter, the Act contravenes the Geneva Convention Relative to the Treatment of Prisoners of War.

The president of the Law Council of Australia, Ross Ray, stated that the continued existence of the facility constitutes a “grievous affront to the rule of law”.

“David Hicks may no longer be held at Guantanamo Bay, but many others remain imprisoned, including some who were literally children at the time of their arrest, more than five years ago. Worse still, there is now the very real prospect that, after several years in secret detention, up to six detainees will be convicted by the US military,” he said.

The legal bodies signatory to the letter together represent hundreds of thousands of lawyers from around the world, including England, Ireland, Scotland, Wales, Canada, Sweden, the Netherlands, Portugal and Romania.