A delay to the publication of the final report of the Chilcot inquiry into Britain's role in the Iraq War has raised suspicions that government departments are trying to prevent it from annexing a number of confidential documents to its conclusions. Were that true, it would be unsurprising. Sir Gus O'Donnell, the Cabinet Secretary, has already vetoed the inclusion of notes between Tony Blair, who was Prime Minister, and the US President at the time, George Bush, on the grounds that publication could inhibit frank exchanges between leaders of the two countries in future.

Such restrictions are doubtless irritating to Sir John Chilcot and his team, but they cannot obscure the important revelations which their work has already prompted. There was much cynicism when the inquiry opened, with many assuming that it would shed about as much light as had the previous four, generally unilluminating inquiries into aspects of the Iraq conflict – from the Commons foreign affairs and security committees and the Hutton inquiry into the death of the weapons adviser Dr David Kelly, to the Butler inquiry, which at least criticised the informal "sofa" style of decision-making that characterised the Blair government.

But Sir John has proved a less malleable creature. From the outset he rejected the recommendation that he take much evidence in camera and insisted on public hearings. Then he called a succession of witnesses, from former Cabinet Secretaries to military commanders, who sharply criticised the way Mr Blair and his close advisers took key decisions without consulting senior ministers and the Attorney General, Lord Goldsmith.

The inquiry has heard evidence that the claim that MI6 had established "beyond doubt" that Saddam Hussein had weapons of mass destruction was "not possible to make on the basis of intelligence". It showed that Mr Blair acquiesced very early on in President Bush's determination to remove Saddam and force regime change. A note from the Prime Minister's private secretary revealed that Mr Blair privately agreed, in October 2002, to commit Britain to war, while publicly suggesting he would use military force only after seeking fresh UN authority.

The Chilcot process has also shown that the Cabinet was effectively excluded from decisions on military action. It proved that Parliament was misled over the strength of intelligence, the severity of the Iraq threat and the legality of the invasion. It disclosed that Mr Blair's private secretary routinely deleted any mention of correspondence with Mr Bush from government minutes. It showed that planning for post-war reconstruction was woeful. And it raised questions as to whether Mr Blair acted honestly when he told his press secretary to blame the French for failures at the UN.

What it has not established beyond doubt is whether Mr Blair just made the wrong judgement calls or whether he acted in bad faith – and lied to Parliament and the nation. The hope is that Chilcot will pronounce on that. It is crucial therefore that the final report should be as full and considered – and well-documented – as possible.

The delay now disclosed may be caused by something as prosaic as the volume of drafting work. But if there is any truth in suggestions that senior civil servants are trying to block the addition of important documents, then ministers must intervene to unblock the process. Conservative politicians may see little advantage in that, since their party overwhelmingly backed Tony Blair at the time. But the Liberal Democrats, who consistently opposed the war, should make it a Coalition priority that the Chilcot inquiry be as unhindered as possible, consistent with national security, in giving a full account of what happened, what went wrong and what lessons must be learnt.