Our Government's decision to go to war in Iraq was based upon an assertion that turned out to be completely untrue. Everybody knows this. In the face of a million protesters on the streets of London, Tony Blair assured us that Saddam Hussein had weapons of mass destruction that he would happily use to threaten our way of life. That's why the dictator had to be stopped, even at the cost of a military invasion.

Whether Mr Blair really believed this is not the point. If he did, he was dreadfully wrong - and the result of this misjudgment was a lengthy conflict with many British dead joining the tens of thousands of innocent Iraqi victims.

Of course, there may have been other, much stronger justifications for Mr Blair's war. But he deliberately chose this one, using his considerable powers of persuasion to precipitate a crisis of confidence in the honesty of all politicians. The result was predictable: finally confronted by the Prime Minister's recklessness, many people convinced themselves that he had long ago secretly agreed in Washington to commit British soldiers to a bloody neoconservative future. What mattered to him was his relationship with GeorgeW. Bush. When they needed to be, Britons would be won over by fair means or foul.

Nobody likes to feel taken in. Enraged by the failure of a system that, if it wasn't dishonest, was surely incompetent, the scene was set for an electorate to believe the worst of all politics. Cash for honours and wars for George were two sides of the same counterfeit coin.

Gordon Brown's decision that the inquiry into the war in Iraq should be held in secret may be a depressing indication that he hasn't yet grasped the depth of damage these events have caused to the relationship between the public and their Government - or the part that a deadening sense of exclusion has played in increasing popular disillusionment. Secrecy has become the addict's shot for irredeemable political insiders who still don't get it. It seems they are not yet ready to grope their way to a cure.

In the US the response to similar public disquiet was different. After wide discussions between the White House, Congress and the broader US public about its form and remit, the 9/11 Commission convened for the first time 441 days after the towers were brought down. Asked by the President and Congress to report on events leading up to the attacks, its members were a bipartisan group of lawyers, academics, former legislators and business figures.

They interviewed more than 1,200 people in ten countries and reviewed more than two and a half million pages of documents, including much highly classified material. Critically, they set about establishing as open a relationship with the American people as was consistent with security. They held many public evidence sessions, which were heavily covered in the press and on television. Much of the testimony was moving and dramatic. In the course of this, the commissioners became familiar to millions as well-known public figures.

Of course none of this guaranteed that their report, published on May 27, 2004, was met with universal acclaim. Many felt that presidents Clinton and Bush had been let off the hook and there was a widespread and sometimes heated debate about the findings. But their determination from the start to hold hearings in public, unless there were strong countervailing reasons to protect classified material, gave Americans a degree of ownership that would have been quite lacking in the face of British-style blanket secrecy. This was not just healthy for the Commission - it was healthy for the US nation as a whole.

The present crisis of trust in British politics is most starkly painted by a collapse of popular faith in the integrity of politicians. A great deal of this loss of belief is ill considered and misplaced, but the nature of our public processes makes any fightback extremely difficult. This is because much of the prevailing cynicism is generated by a sense that the public do not count. There is a deep feeling that our democracy is not participatory and that government is unhearing and hidden from view: yet Westminster seems unprepared for real change. This is indeed a surprising moment to assert that a secret investigation is compatible with public confidence. And reaching back to 1983 for a precedent in the Franks Report into the Falklands conflict is hardly reassuring. Is it really necessary to point out how much has changed in our public life over a quarter of a century?

And the world has changed too. People have become accustomed to information. They like it - and expect to access it with their fingertips, consuming explanations whenever they want. The internet is the enemy of secrecy.

The Prime Minister's statement on Monday was an opportunity for Parliament to demonstrate deep and serious reforming intent. It could have indicated precisely the commitment to cultural change that public anger over expenses has been crying out for. An announcement that, with all-party agreement, the nation would have its open inquiry, as transparent as possible and properly managed for early reporting, would have been an important signal of emancipation. This could, of course, have been achieved if the will had been there. A nation that can organise a war can certainly organise an investigation.

But such an announcement would have done much more. It would also have hailed the obvious - that however distinguished the men and women appointed to conduct this grave work, the public are no longer prepared to be treated as outsiders peering over the gates into their own mysterious country.

Ken Macdonald, QC, practises at Matrix Chambers and is a visiting professor of law at the London School of Economics 2009-2010. He was Director of Public Prosecutions 2003-08

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