Even amongst Liberal Democrats, I've a reputation as something of a constitutional anorak.

Thus, observing the referendum debate, the passion it has inspired, has for me been invigorating. The polls now suggest the outcome is very much in the balance. Great efforts are now being made to emphasise proposals for greater devolution for Scotland. This is great news and a fantastic opportunity. We could, and should, go further, and make government responsive to everyone in these isles.

I have hope that, if Scots choose not to separate from the UK, that we can tap into the campaign's energy and commitment. The referendum's impact has gone beyond Scotland; it is stirring the slumbering desire for democratic renewal elsewhere in the UK. People are looking north, and asking why they too can't make more decisions for themselves. This is the right time to reassess the system of government for the whole of the UK.

But without the benefit of a written UK constitution, we lack a defined route to reform. In the past, constitutional changes have evolved sometimes slowly, as with the extension of the franchise, sometimes more rapidly, as with the incorporation of the European Convention of Human Rights into our domestic law and the Freedom of Information Act.

How best then, should we move forward, convert this energy into action, this pent-up demand into change? And what issues must be addressed?

To build agreement on what form a renewed UK should take, to ensure reform makes our governance structures work for people, change needs to be carefully considered. This should be about more than what constitutional changes the incumbent party of government happens to prefer; it must be about people as citizens. We need a forum for debate and public participation, so evidence can be put forward and outcomes agreed on a broad basis. Enabling the public to offer its best input into decision-making is surely the essence of democracy.

Now, what does that sound like? Fortunately, we have the useful, successful and wise precedent of the Scottish Constitutional Convention, which led to the setting up of the Scottish Parliament.

Thankfully, there are now indications that the UK parties favour a similar approach. But to address the issues in the round there needs to be UK-wide convention. One of the difficulties arising from the Scottish Parliament being established without a conversation about its impact on the rest of the UK, is the West Lothian Question, having Scottish MPs able to vote on England-only legislation but not vice versa. A constitutional convention of the UK would help ensure that issues were considered in the round so that such anomalies did not arise.

A deliberative Constitutional Convention for the United Kingdom should replicate the participative model in Scotland, and the public engagement seen during the referendum campaign. Its membership should not be confined to politicians but open to business people, trade unionists, civic representatives, academics and lay people.

Such an approach would have great advantages. Critically, it would ensure that changes commanded the support of a broad swathe of citizens, politicians and key interest groups, just as the Scottish parliament is the "settled will" of the Scottish people.

If a UK constitutional convention is the means, what is the end? At this point, we should avoid being prescriptive about the outcomes, but focus on the issues reform must address.

It is notable that neither in Scotland, nor elsewhere in the UK, has there been any accretion of powers to the localities. Politicians hanker after power and they will grasp it if they can. That is why we have witnessed so much centralisation in Scotland and elsewhere around the UK. A convention on the future government of the UK should include a requirement to consider not just the top levels of power but how it can be devolved further, closer to people, to bodies such as national, regional and local government. Political decisions need to be taken at the lowest level at which they are effective - the constitutional principle of "subsidiarity".

The translation of that excellent principle into a suitable constitution requires careful thought. Such a written constitution would include substantial extra powers for the Scottish Parliament, Welsh Assembly, for the national or regional tier in England and for local authorities throughout the UK. With such greater devolution, a UK Constitutional Convention must also address the necessary consequential changes to the Westminster Parliament. It ought to consider systems of voting to ensure that minorities are heard.

Similarly, what cannot be achieved at local level should be entrusted to levels above. There is a balance to be struck here. A community that decides to invest in, say, improved transport, or skills development, or the exploitation of local resources, should have the power to do so. But there needs to be dialogue with other levels of government to ensure there is no wasteful overlap.

The outcome of a UK Constitutional Convention, if it follows the principle of subsidiarity, would very likely be a modern Federation.

A further key issue to be addressed is responsible governance. Put simply, each of the different tiers of government should raise the bulk of the money they spend. It is a flaw in the present arrangements for the Scottish Parliament that this is not the case. Rectifying that, and indeed at all levels of government across the UK, will mean that people can truly hold those they elect responsible.

Amongst the primary advantages of the UK are the opportunity to pool resources for common goals and the economic security it can offer in bad times. A key role for central government should be redistributing its resources to areas of the greatest need, as a replacement for the current Barnett formula.

For this reason, and because central government will continue to have responsibilities that it makes no sense to try to devolve, the UK tier should continue to be responsible for raising its own funding.

As it distributes resources according to need, the UK tier also extends opportunities to all, a process that began after the Act of Union in 1707. Scots were then able to start sharing in the growing commerce of England across the world. The success of that Union was exemplified by the diaspora of Scots to the Empire and by the golden age of intellectual and cultural pre-eminence in Scotland itself. The Scots and the English grasped the benefits of inter-dependence.

That great Scot, John Buchan, when he was Governor General of Canada in the 1930s, feared that the different interests of the scattered Canadian population might lead to alienation of one province from another. As his biographer, Janet Adam Smith, pointed out, "He emphasised how natural it was to the Scot to hold multiple loyalties - to Highlands or Borders, Edinburgh or Glasgow - within the loyalty to Scotland; to Scotland within the loyalty to Britain. 'A man can never have too many loyalties' Buchan told an audience on Prince Edward Island."

That remains true today. We have a chance to seize the opportunity created by the referendum. From turbulence we can build certainty. Now is the time for a constitutional convention for the UK.