It is the DUTY of all citizens to attempt to apprehend anyone contemplating crimes against humanity. This is the major lesson of the Nuremberg trials. I have posted below just one segment of the various articles that list what constitutes such a crime. As you can see in (a), just planning a war of aggression is a crime. And yes, every president and PM since WW2 is guilty of that. But what concerns us now is the present moment. These people are criminals; if they are allowed to go on, they will certainly compound the crimes they have already committed. No one is above the law, and there is no "diplomatic immunity" for these types of crimes. Any citizen can draw up a semi-formal arrest warrant to apprehend those of the Bush or Blair administration suspected of violating laws against humanity.

 http://www.yale.edu/lawweb/avalon/imt/proc/imtconst.htm

Article 6.
The Tribunal established by the Agreement referred to m Article 1 hereof for the trial and punishment of the major war criminals of the European Axis countries shall have the power to try and punish persons who, acting in the interests of the European Axis countries, whether as individuals or as members of organizations, committed any of the following crimes.

The following acts, or any of them, are crimes coming within the jurisdiction of the Tribunal for which there shall be individual responsibility:

(a) CRIMES AGAINST PEACE: namely, planning, preparation, initiation or waging of a war of aggression, or a war in violation of international treaties, agreements or assurances, or participation in a common plan or conspiracy for the accomplishment of any of the foregoing;

(b) WAR CRIMES: namely, violations of the laws or customs of war. Such violations shall include, but not be limited to, murder, ill-treatment or deportation to slave labor or for any other purpose of civilian population of or in occupied territory, murder or ill-treatment of prisoners of war or persons on the seas, killing of hostages, plunder of public or private property, wanton destruction of cities, towns or villages, or devastation not justified by military necessity;

(c)CRIMES AGAINST HUMANITY: namely, murder, extermination, enslavement, deportation, and other inhumane acts committed against any civilian population, before or during the war; or persecutions on political, racial or religious grounds in execution of or in connection with any crime within the jurisdiction of the Tribunal, whether or not in violation of the domestic law of the country where perpetrated.

Leaders, organizers, instigators and accomplices participating in the formulation or execution of a common plan or conspiracy to commit any of the foregoing crimes are responsible for all acts performed by any persons in execution of such plan.