That once-happy band of constitutional reforms is not quite the young and virile gang it used to be. Devolution is sullenly nursing its pint somewhere in the north-east of England surrounded by lack of interest. Lords reform is dithering. And proportional representation seems to have wandered away in a fit of absent-mindedness.

It is a depressing scenario for all those, such as myself, who pushed so hard for the fundamental change that the late 1990s seemed to promise. We cannot overlook the real achievements of those years - devolution, the Human Rights Act, abolition of hereditary peers in the Lords. But equally, we cannot pretend that this agenda can simply be picked up, unchanged, from the place where Tony Blair dropped it.

That agenda was about inscribing the principles of accountability, equality and dispersal of power at the heart of our political system. For years, reformers concentrated on the threat to those ideals from an overpowerful and self-interested political centre in Westminster. What we didn't notice was the other danger creeping up behind us: political disengagement.

The reformer's defining myth of a government wresting power from the hands of its resistant citizens is no longer quite right. A more appropriate image may be that of an unchecked government wielding power with insufficient challenge, while a cynical public looks on. We risk a situation where not only are the people disengaged and disaffected from politicians, but politicians are disengaged and disaffected from the people. A lengthy era of mutual distrust and incomprehension may beckon.

How else can we explain the fact that this government has presided over the two lowest general-election turnouts alongside the two largest street demonstrations in the postwar era?

We all know that steep decline in voter turnout has made some politicians sit up and take notice. But they can't really plead ignorance. Political parties - so central to maintaining the link between people and power - have been losing members for 40 years or more. The three main parties now have less than a quarter of the members they had in 1964. Voter turnout might bounce back, but the parties are a few breaths away from a death rattle in many constituencies.

So disengagement is not a short-term blip. The similar declines in party membership and voter turnout that have been occurring across most of western Europe should start ringing alarm bells about the deep social causes of this problem.

At root, this may be about the changes that the older democracies have undergone since the 1960s. We have a system of parliamentary representation based on hierarchy and deference to the superior understanding of your betters in the Commons. And we have parties split along lines that reflect the class identities and values of the industrial age.

But since this system established itself in the early 20th century, there has been a social and cultural revolution. Deference died in the late 1950s; the population became increasingly well educated and began to believe in the value of its own views and lifestyles; and the sharp class distinctions of the industrial era withered, as the service sector became the powerhouse of the UK's economy.

Fundamentally, individuals have come to expect a high degree of control over the services and products that shape their lives. The notion that this control can be delegated upwards to a "superior" official - elected or otherwise - goes against the grain of the social and cultural change of the past 40 years. With such a dichotomy between our political system and our social and cultural values, is it any wonder that disengagement and disaffection are the long-term results?

The good news is that I am not the first to recognise the danger that this poses. The Rowntree Trusts have set up an inquiry ("Power") to investigate how political participation in Britain can be reinvigorated. There will be a commission at the heart of the inquiry but there will also be a major research programme and a series of public engagement events running alongside the commission's deliberations.

As chair of the commission, I take heart from the knowledge that I will not be peering into a vacuum. There is a huge amount of good practice and many exciting ideas designed to re-engage with the public, listen to their views and give them a real say in the decisions that affect their lives. Whether it is through citizens' juries, participatory budgeting, or simple but genuinely open consultation, there is already a wealth of local initiatives aimed at winning back some of the legitimacy that straightforward representative dem-ocracy has lost in recent years.

And, after all, what better guarantee is there of accountability, equality and dispersal of power than a truly engaged and active citizenry?

To find out more about Power, visit www.powerinquiry.org (telephone: 0845 345 5307)