The United States of America has not accepted the court's jurisdiction and also Iraq is not a States Party. The United Kingdom became a States Party on 4th October 2001. The court only has the jurisdiction granted to it by the Rome Statute on the International Criminal Court - see ICC website - jurisdiction and Court's Statute.
The court's jurisdiction:
The Court does not have universal jurisdiction.* The Court may only exercise jurisdiction if:
The accused is a national of a State Party or a State otherwise accepting the jurisdiction of the Court;
The crime took place on the territory of a State Party or a State otherwise accepting the jurisdiction of the Court; or
The United Nations Security Council has referred the situation to the Prosecutor, irrespective of the nationality of the accused or the location of the crime.
It would seem that only the first of those points applies to Blair. Bush would seem to be completely safe from the tentacles of the court.
Furthermore, the ICC has no power to act in relation to events before 1st July 2002. Note also the principle of "complementarity."
The Kamapala conference also agreed that the Court will not be able to exercise its jurisdiction over the crime of aggression until:
· at least 30 States Parties have ratified or accepted the amendments; and
· a decision is taken by two–thirds of States Parties to activate the jurisdiction at any time after 1 January 2017.