Tony Blair is facing a formal complaint to the international war-crimes tribunal by a panel of senior international legal experts for unlawfully waging war in Iraq.
Full story here. The charges focus around specific violations of the Geneva conventions and international human rights treaties, leading to excessive numbers of avoidable civilian deaths. Not as good as a simple charge of aggression, but the ICC isn't currently prosecuting those.
Unfortunately, the true architects of the invasion of Iraq - Bush, Cheney, and the NeoCon cabal - are beyond the ICC's jurisdiction. But the United Kingdom is a signatory, and Blair is well within their reach. He certainly has a case to answer; it's just a question of whether the ICC will live up to its mandate to prosecute crimes against humanity, or whether it will be subverted into another rubberstamp body for the major powers.