So at last we know – or at least we know a little more than we did. After resisting calls for a timetable, Sir John Chilcot, the head of the Iraq inquiry, has now said his report will be finished in April and that it will be published in June or July 2016. The official reason for the two-month gap between the report being finished and publication is that it has to be checked over for any issues of national security, although it feels like another yet miserable delay in a sorry saga, particularly when the Prime Minister says the security checks could be completed in a fortnight.

Looking back, it is hard to believe that the report really has taken this long (the inquiry was ordered by Gordon Brown in 2009 and the formal evidence gathering ended four years ago). No one expected it to be quick - Sir John's inquiry had an unprecedented scope ranging over every aspect for the Iraq war, including the build-up and its aftermath, so it was never going to be speedy. Indeed, tasked with providing the definitive account of the war, Sir John was right to take time and examine the subject thoroughly and forensically.

However, the delays to publication have been frustrating and hard to fathom. The first stumbling block was the lengthy wrangling over the publication of correspondence between Tony Blair and George W Bush that centred on British involvement in the conflict and in particular the question of whether Blair provided any undertakings to Bush in the run-up to the invasion. Eventually, a deal was struck to publish the gist of the letters rather than the details, which allowed the inquiry to move on but raised serious concerns that it will be too much of a compromise.

The question of the Bush/Brown letters also led to even more delays as the inquiry began to send sections of the report to witnesses, including Tony Blair, and allowed them to respond. Even if this had to be done, there was no sense of urgency about the process and it has only served to deepen the concerns about compromise.

Everything must now be done to expedite the process - not least because of the distress to the relatives of servicemen and women, but also to preserve any remaining public confidence in the process. Sir John was given a huge task in 2009 and his report will succeed or fail on how directly it tackles the big questions. The biggest of them is the Labour government's dubious justification for the war – weapons of mass destruction – which has prompted Hans Blix, the UN's former chief weapons inspector, to claim in an interview this week that the Blair government's actions amounted to misrepresentation. Just as important is the question of the post-invasion chaos. All of these questions, and more, will have to be answered by the report. It is ridiculous that we have had to wait this long for it – but the wait had better be worth it.