The High Court is ruling on whether a former chief-of-staff of the Iraqi army can bring a private prosecution against Tony Blair over the Iraq war.
General Abdul Wahed Shannan Al Rabbat alleges Mr Blair, then UK prime minister, committed "the crime of aggression" by invading Iraq in 2003 to overthrow President Saddam Hussein.
The general wants to prosecute Mr Blair and two other key ministers at the time - foreign secretary Jack Straw and the attorney general, Lord Goldsmith.
Westminster Magistrates Court refused to issue summonses in November last year on the grounds that the ex-ministers had immunity from legal action, and in any event the current Attorney General, Jeremy Wright QC, would have to give consent.
The general is applying to the High Court in London for a judicial review of the magistrates court decision.
The general lives in Muscat, Oman, does not possess a passport and cannot travel to the UK.
The Attorney General intervened in the case and his legal team urged Lord Thomas of Cwmgiedd, the Lord Chief Justice, sitting with Mr Justice Ouseley, to block the general's legal challenge on the grounds that it was "hopeless" and unarguable because the crime of aggression is not recognised in English law.
The UK was part of the coalition led by the US which invaded Iraq after US president George W Bush and Mr Blair accused Hussein of possessing weapons of mass destruction and having links to terrorists.
Michael Mansfield QC, appearing for General Al Rabbat, said at a recent hearing that the inquiry into the invasion conducted by Sir John Chilcot, which concluded with a report published in July last year, justified the prosecution of Mr Blair.
Mr Mansfield said the main findings were contained in a paragraph early in the 12-volume report and could be summarised as concluding that Hussein did not pose an urgent threat to the interests of the UK, and the intelligence regarding weapons of mass destruction had been presented with "unwarranted certainty".
It also concluded that peaceful alternatives to war had not been exhausted and that the war in Iraq was not necessary.
The report found that the US and UK had undermined the authority of the UN Security Council by invading without its authority.
Mr Mansfield told the court: "Nothing could be more emphatic than this evidence.
"It does not say there was an unlawful war or crime of aggression.
"It doesn't need to because the criteria are arguably all there in that paragraph."