AMID the many uncertainties about Scotland's future, two things are clear: a referendum is imminent and independence will be on the ballot.

Both supporters and opponents of independence should be candid about what is at stake here. Independence is not simply another piece of constitutional tinkering. It is not a minor amendment to the Scotland Act, aimed at improving the territorial management of Scotland within the Union. It means nothing less than the abolition of the United Kingdom and the creation of a Scottish state.

If the history of the 20th century teaches us anything, aside from the superiority of liberal democracy over all forms of closed and tyrannical society, it is that independence and freedom are not synonymous. Many countries have won their independence only to become "entangled again with the yoke of bondage". In Burma, Pakistan and Zimbabwe, to name but three, the struggle for statehood has been followed by periods of instability and violence, marred by one-party dictatorship or military rule. The "success stories" of independence, such as Norway, Finland and the Baltic states, in contrast, have been characterised by their ability to build lasting "free institutions". Thus, if Scotland is truly to flourish, we need much more than independence: we need a robust democratic polity, with an open, representative, accountable and constitutional form of government. We need to buttress our democratic ethos with strong civic institutions through which the common good can be discerned and realised.

The game has changed. The days of flag-waving, consciousness-raising, symbolic nationalism are over; the time for state-building has begun. The constitutional debate in Scotland must move on from its longstanding obsession with Scotland's relationship to the rest of the United Kingdom (in the event of a Yes vote, this will become a matter of foreign policy).

It is time to shift our focus on to the design of a new Scottish constitution, outlining the principles and structures of the state through which Scotland will govern itself.

It is here that Scotland can distinguish itself from the Westminster legacy. The Scottish independence movement does not merely oppose rule from Westminster. It has, for decades, also opposed the Westminster way of ruling, which is associated with excessive secrecy, hidebound procedures, exclusivity, and the dangerous concentration of power in the hands of the Prime Minister. Motivated by civic and democratic principles, supporters of independence have long adhered to a tradition of the sovereignty of the people. This tradition, which can be traced to the Declaration of Arbroath of 1320, relies on the moral principle that government is instituted by, and for, the "whole community of the realm". Similar principles can be found in the Reformed tradition, with its concern for "covenanted" relationships based on mutual responsibility and the limitation of all power by law.

Principles are important. They set out what the state is for, and give the people a yardstick by which it can be measured. The Swedish constitution, for example, states that all public power "proceeds from the people" and should be exercised "with respect for the equal worth of all and the liberty and dignity of the individual". Universal and equal sufferage are to be the foundations of democracy, and it stresses that the personal, economic and cultural welfare of the individual shall be fundamental aims of public activity.

"In particular," it adds, "the public institutions shall secure the right to employment, housing and education, and shall promote social care and social security, as well as favourable conditions for good health."

The UK, in contrast, has always shied away from such principles, in favour of merely pragmatic pacts between competing elites. Uniquely among the nations of Europe, the UK stumbled into democracy without pausing to adopt a written constitution. Instead, we got a "sovereign parliament", whereby the aims and processes of the state, and the rights and liberties of citizens, are alterable at will by the Westminster parliament, limited only by ordinary law, custom, precedent, tradition, or treaties.

According to the SNP's most recent elaboration of its constitutional policy, an independent Scotland would change all that: "In line with practically every other country in the world [Scotland] will have a written constitution." This, it continues, "is necessary to protect the rights of every Scottish citizen and to place restrictions on what politicians can and cannot do. A written constitution for a free Scotland provides us with an opportunity to enshrine fundamental human rights in Scotland's basic law and ensure a government truly accountable to the people of Scotland."

If an independent Scotland is to achieve its full potential, its constitution should incorporate the best practices of other leading European democracies, and particularly those of the Scandinavian countries. This means building on the vision set out by the Constitutional Convention in the 1990s, which insisted that Scotland should not only have its own parliament, but should have a different type of parliament – a Scandinavian-style parliament, with more active control over legislation and policy-making, more meaningful and informed debate, stronger committees, and a more egalitarian, democratic and transparent ethos.

In keeping with these traditions, principles and aspirations, the SNP has prepared a detailed constitutional policy. The late Neil MacCormick, its principal author, described these ideas as the "common stock of democratic thought in Scotland today" – the foundation on which the Scottish state must be built. According to the SNP's plans, there would be a written constitution, endorsed by a referendum, and capable of being amended only by a three-fifths majority of Parliament followed by a referendum. This would include an extensive list of guaranteed rights, modelled on the European Convention on Human Rights, but also including certain socio-economic rights such as entitlement to healthcare and education. These rights might be restricted by law during a state of emergency, but any declaration of a state of emergency would have to be confirmed by a three-fifths majority of Parliament within two weeks, and continuation of the state of emergency may not be prolonged for more than three months without further parliamentary approval.

Acts of Parliament that are incompatible with the fundamental rights, or any other part of the constitution, could be annulled by the judiciary – for example, a bill to extend the life of Parliament indefinitely, or to deny the right to vote to a minority group, would surely be deemed unconstitutional. This is not, as detractors might claim, an undemocratic judicial power, but a democratic power that places the higher law enacted by the people above the subordinate law enacted by their representatives. To prevent politicisation of the judiciary, judicial appointments would be made on the binding advice of an independent commission on judicial appointments, which would include senior members of the legal profession together with lay members elected by Parliament. The judges would be removable only by a two-thirds majority of Parliament on the grounds of misconduct.

The monarchy would be retained as a ceremonial figurehead (as the queen of Scots), but its prerogatives would be curtailed. Executive powers would be vested in a council of ministers responsible to Parliament, with the Prime Minister of Scotland being formally elected by a parliamentary vote. The government would be limited in size to a maximum of one-fifth of the total size of Parliament, so as to limit the "payroll vote" and restrict the Prime Minister's powers of patronage.

Proportional representation would be used for all parliamentary and local elections, with the voting age reduced to 16. The Parliament would be unicameral. In place of a second chamber, a minority veto procedure, modelled loosely on that of Denmark, would enable 40% of the membership to suspend a bill, other than a money bill, for between 12 and 18 months. During this period of suspension, the majority could overturn the veto by putting the bill to the people in a referendum.

Parliament would sit for fixed four-year terms; it could be dissolved before the completion of its term only if a prime minister could not be appointed. This would prevent the prime minister from playing cat-and-mouse with election dates. The draft constitution includes measures to ensure public scrutiny, including the right of parliamentary committees to conduct public hearings on proposed legislation. Parliament would also have control over declarations of war and the ratification of treaties. Treaties delegating powers to the EU or other such institutions would be subject to approval by a three-fifths majority vote in Parliament followed by referendum.

As it currently stands, the SNP's draft constitution is far from perfect and would benefit from careful revision. It makes no provision, for example, for an ombudsman or auditor-general. The electoral system is poorly specified, and there is no electoral commission to prevent gerrymandering. Its provisions concerning parliamentary privileges and procedures are sketchy at best. Nevertheless, the contrast between the provisions of the SNP's draft constitution and the tangled mess of the British system is clear.

This provides an opportunity to the pro-independence side. If it can expose the flaws of the British system of government and explain the benefits of having clear principles established in a written constitution, then it can make a moral and democratic (rather than purely identity-based or economic) case for independence. There are Greens, disaffected Liberal Democrats and many others in Scotland for whom a written constitution, better democracy, and guaranteed rights have long held appeal. Connecting with these voters, and showing them why democracy in an independent Scotland would outweigh any advantages of British rule, might be crucial to the Yes camp.

Perplexingly, the SNP have been slow to capitalise on these advantages. They have been bashful about the details of their constitutional policy, and have not always given clear or consistent messages. Senior party figures, while endorsing the principles of the draft constitution, have yet to be drawn publicly on the details. The elaboration of a new constitution for Scotland appears to have been postponed until after independence.

In some ways, this postponement is understandable. It reflects a desire to focus on independence without the distraction of other, seemingly post-independence, issues. In other ways, however, it indicates a worrying lack of constitutional concern and awareness among senior civil servants, parliamentarians and other policymakers; an inability to appreciate the fundamental difference between a "sovereign Scottish Parliament" and a "sovereign Scottish people"; a misplaced belief that the mechanics of constitutional design are irrelevant; or a cavalier expectation that the "fiddly details" of constitution-making might best be left to the discretion of the lawyers.

Postponing the design of a Scottish constitution until after independence is a risky course of action. A newly-independent Scottish state will suddenly have to deal with several immediate and practical problems, ranging from the establishment of embassies and the organisation of the armed forces to the issuing of stamps. Good constitutional design, so essential to the health of our polity, is likely to be overlooked in the rush.

This failure to "grasp the thistle" of constitutional design, ahead of any referendum on independence, would enable the opponents of independence to claim (with some justification) that independence would be hazardous, as it would hand over indeterminate power to the Scottish Government without any thought of the consequences. It would be easy for Unionists to say that the implications of independence have not been properly thought through. Delay also increases the danger of ending up with a poor quality constitution, thrown together by the negotiating teams and based on a relic hastily produced from an old Colonial Office file.

The time to build a broad consensus around an agreed Scottish constitution is now, before a referendum on independence is held. This ought to be a matter of priority for the Scottish Government, for the SNP, and for all who support independence. It ought also to be given due consideration by those who would rather not see an independent Scotland but who, if it happens, want to make it work. By working out the details of a new democratic constitution in advance of the referendum, we can help to ensure that an independent Scotland – if that is what the people desire – will take its place alongside our Scandinavian neighbours in the "arc of democracy".

W Elliot Bulmer is research director of the Constitutional Commission. His forthcoming book, A Model Constitution For Scotland: Making Democracy Work In An Independent State, will be published next month by Luath Press, Edinburgh. Advance copies are available now, priced £9.99, by contacting info@constitutional