Controversy revolves around then prime minister’s decision in 2003 to take Britain into the invasion.
A high court judge is to consider whether a legal ban on prosecuting Tony Blair over the Iraq war can be challenged.
A private criminal prosecution against the former Labour prime minister was blocked in 2016 when it was ruled Blair would have immunity from any criminal charges.
On Tuesday the high court will consider arguments for reversing that ban and for keeping it.
The attorney general, the government’s top law officer, wants the ban upheld and also to join the case.
The current controversy revolves around Blair’s decision when prime minister to take Britain into the invasion of Iraq in 2003, which was led by the United States and sparked huge opposition.
In November 2016, a British court ruled against an application to bring a private prosecution. A district judge at Westminster magistrates court ruled Blair had immunity from prosecution over the Iraq war and that any case could also “involve details being disclosed under the Official Secrets Act”.
The attempted private prosecution was brought in the name of a former top Iraqi general and sought to try Blair for the crime of aggression. On Tuesday, a more senior judge will consider whether there are sufficient grounds to grant a judicial review of the rejection of the prosecution.