Leading article: The revelation has been in the detail

Tomorrow, the Chilcot inquiry into Britain's decision to go to war on Iraq will have sat for a whole year. It has been a suprisingly worthwhile exercise, bringing to full public view a depressing picture of the way the country was led to war against the advice and warnings of most of the experts and officials at the time. But the steady drip-drip of its evidence has served largely to confirm what many people suspected, rather than revealing anything startlingly new.

George Bush and Tony Blair were set on regime change in Iraq from very early on, before July 2002. Mr Blair misrepresented the nature of the claim that Iraq could deploy weapons of mass destruction within 45 minutes. There was no proof of any links between al-Qa'ida and Saddam Hussein. The British Attorney General, Lord Goldsmith, was "leaned on" to change his opinion on the legality of the invasion. The Cabinet was kept in the dark on many details.

There have been some interesting shifts of nuance: the former UN weapons inspector Hans Blix, who had been portrayed as believing that Saddam had no weapons of mass destruction, testified that, though his doubts grew, he still advised Mr Blair fairly late in the day that Saddam probably did still have them. There have been attempts at back-covering and personal apologia. There have been differences of interpretation: the former top general Sir Richard Dannatt yesterday claimed that the army was close to seizing up in 2006 when Mr Blair intervened again in Afghanistan while British troops were still in Iraq; by contrast, Mr Blair told the inquiry that the generals advised him that fighting in two theatres of war was tenable.

Sir John Chilcot's brief is to examine the way decisions were made and actions taken and identify lessons for the future rather than apportion "blame". Some of that will be fairly detailed, as with General Dannatt's suggestion yesterday that Britain should probably have embedded trainers with Iraqi security forces much earlier than it did. But though Chilcot will provide a lot of primary source material for historians, it is hard to now see that it casts new light on the most basic political question of whether the war was a good idea. It has just not uncovered a new smoking gun.

Some have suggested the inquiry team are at fault in that. Carne Ross, the UK's Iraq expert at the United Nations from 1997 to 2002, has claimed that the Chilcot team have been insufficiently rigorous in grilling those called to give testimony. It has repeatedly failed to challenge witnesses on contradictions between their testimony and the evidence of documents it has uncovered. Moreover, Mr Ross claimed that the Foreign Office has withheld key documents he needed to give proper evidence to the inquiry.

For all that, Chilcot has been a useful platform in which witnesses like Eliza Manningham-Buller, the former director-general of MI5, could contradict the oft-repeated New Labour nonsense that the war in Iraq did not render a generation of young British Muslim men more susceptible to radicalisation. Whether much use will be served by Sir John Chilcot's decision earlier this month to extend the time for submissions from international lawyers – on the legal justification for the 2003 invasion – is another matter. What we want from Chilcot is new facts, not more lawyers' opinions.

The lack of decisive new evidence now severely constrains Sir John's options. If his final report broadly absolves Tony Blair from the charges of deliberately misleading Parliament and undertaking an "illegal" war, it will be considered a whitewash. If it does not, there will be those who will dismiss it as a kangaroo court. Unless there are further witnesses with something substantively new to say, it is probably now time for the inquiry to be drawn to a conclusion.