The coming to life of the campaign for proportional representation since the general election is an important factor in the debate about the state of democracy in 21st-century Britain, but it needs to be seen as only part of that debate.

On its own, the introduction of PR is unlikely to cure all the ills of a tired political system; a system which the public are telling the politicians is well past its sell-by date; a system which resulted in a government winning with a majority of 67 when just 21.6 per cent of the electorate actually voted for it and with the support of only 36 per cent of those who did vote.

What Tony Blair's government has demonstrated, in particular by the way the decision to go to war in Iraq was taken, is that while a change in the voting system is necessary, it is unlikely, of itself, to be enough to counteract the changes to our democratic system over the past quarter of a century. What is needed if democracy is to flourish is a comprehensive debate about the whole nature of our democracy - culminating, if that is what the public want, in radical change.

In the 30-odd years I have followed politics, our system of government has slowly but surely changed from cabinet government to the neo-presidential system we have today. What Mrs Thatcher and later, and to much greater effect, Tony Blair have both demonstrated is that a powerful - some would say ruthless - leader with a big majority in the Commons is largely unaccountable in our political system.

Looking back now, we can see that from the very beginning Tony Blair was determined to rule without proper cabinet discussion - in all areas, that is, except the economy where, it seems, Gordon Brown has been equally dominant. One of the Blair government's first decisions in power was to go ahead with the Dome, despite the fact that the majority of the Cabinet were against the project.

But the Dome was small beer compared with Iraq. Nothing illustrated Blair's ever-increasing control more clearly than the way the decision to go to war in Iraq was taken by a Prime Minister who was able to delude himself and the nation that third-rate intelligence on Saddam's WMDs justified going to war.

What is remarkable is not that the Prime Minister tried to suppress the information and subsequent debate in Cabinet, but that his colleagues allowed him to get away with it. Members of his Cabinet - with the notable exceptions of Robin Cook and, to a lesser extent, Clare Short - should look back on their failure to ask the right questions and to ask for the relevant documents with shame.

In doing so, this Cabinet failed to fulfil one of its central roles in the British democratic system - to hold the Prime Minister in check. As a result, we've had government without one of the essential checks and balances.

Lord Butler, the former head of the Civil Service who chaired the committee which looked into the intelligence failures in the lead-up to the war in Iraq, summed up the failure of cabinet government in a recent interview with The Spectator: "The Cabinet now, and I don't think there is any secret about this, doesn't make decisions ... What happens now is that the Government reaches conclusions in rather small groups of people, and there is insufficient opportunity for other people to debate, dissent and modify."

In the same interview, Lord Butler also pointed up the second major failing of democracy in the time of the Blair government - the failure of the legislature to hold the executive in check. Any interest group or lobbyist trying to change a bad Bill knows only too well that their best chances are in the unelected House of Lords, where the Government whips are less effective and debate is more intelligent, rather than in the Commons where, in the last parliament, some terrible legislation was passed on the nod, pushed through by the whips.

What is perfectly clear is that many of the failures of our democratic system as shown up by the Iraq saga are directly related to the Prime Minister's power of patronage. The House of Commons is full of Labour MPs anxious to get on, and under the British system they can only do so by appealing to their party leaders. Watching a series of Labour MPs churning out the Downing Street line on Iraq was pitiful, but of course the reason they were prepared to do it was that the Prime Minister and those around him controlled their futures.

In most areas of life, if you don't get on with the boss or don't think you are making progress, you just change your job. In politics there are no other jobs to go to, hence the power of patronage.

When in a decade or so historians take a long hard look at the Labour government of 2001-05, and come to terms with what the Iraq adventure meant, it could well be that the past four years will be seen as a turning point in British democracy. With pitifully low turnouts at two consecutive elections, widespread apathy about politics in general and a deep mistrust of, and sense of betrayal by, the Prime Minister, something has to be done.

So what do we need to change? Well it could be that Mrs Thatcher and Tony Blair were right in identifying that we need strong leaders who can take decisions in the world we now live in; maybe we do need a presidential system. But if that is the case, we need the checks and balances that go with it. Perhaps we should have a directly elected Prime Minister serving for a maximum of two specific terms? Perhaps it is time to separate the executive from the legislature so that the Cabinet is not chosen from the very same people who also have the role of holding the executive in check? Perhaps we should follow the Australian system of compulsory voting? Perhaps we should have an elected House of Lords with no whipping system? And of course we will need proportional representation, if for no other reason than to assure every voter that their vote does matter.

What we need now is a serious commission appointed by Parliament, but not made up exclusively of parliamentarians, to look at our constitutional settlement, to examine how our democracy works, and to come up with recommendations for change. That needs to report not to the government of the day - turkeys don't vote for Christmas - but to Parliament.

And then it's up to us. Of course everyone will say it can't happen, that we, the people, can't get radical change on the scale needed, that the mythical "they" won't allow it. But events in France and Holland this week have shown that there are times when the people can overthrow the political élites, that there are times when they can demand and get radical change.