THIS column has consistently argued that Scotland needs a written constitution. This is not an optional extra. It is a prerequisite of statehood and foundational to the independence project.

I have repeatedly insisted that work on constitution-building should begin at once, so that an agreed constitution can be presented to the people before the next independence referendum and – if endorsed by the people in the referendum – can come into effect immediately on independence day. That way, everything will be clear and above board. There will be no dangerous legal gaps, no blank cheques of unlimited power, and no constitutional black holes.

All this must be done to ensure certainty, security and reassurance during the transition to statehood, and to buttress the unity and democratic legitimacy of the new Scottish state during the perilous first years of independence.

However, as SNP president Michael Russell argued in a recent article in The National, we cannot pre-emptively impose answers to every constitutional question, nor definitely determine the future shape of Scotland from the get-go.

One of the strengths of the pro-independence movement is that it is socially and ideologically diverse. It includes members who are middle class and working class, urban and rural, socialists and neo-liberals, radicals and moderates, progressives and traditionalists, religious and secular, monarchists and republicans.

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If the constitution is supposed to be some kind of blueprint for utopia, not all these groups will be able to agree on what that looks like. The SNP have often feared, and not perhaps without reason, that making overly specific constitutional commitments risks undermining the fragile unity of this heterogenous coalition.

There is also the matter of public and cross-party engagement.

Any constitutional draft developed before the next referendum might embody a sufficient consensus amongst those who support Scottish independence, but it will not have input from the other side – those who find Scottish independence a threat either to their identity or their interests.

A final settlement of the constitutional question, if it is to produce an inclusive and lasting constitutional order, will have to include these voices: Tories, too, are part of Scotland.

So here is the problem: we have to do something now, but cannot do everything now. This naturally calls for a two-stage constitutional process.

The first stage would be the development of a constitution, to be agreed within the Yes movement, approved by a resolution of the Scottish Parliament, and presented to the people in the next independence referendum.

This constitution would come into effect on independence day as the supreme and fundamental law of Scotland. It would have, however, only provisional status. It would contain provisions setting out a second stage of constitution building, after the dust of independence has settled, by means of a democratic, participatory and inclusive process.

At the first stage, what matters is getting a provisional constitution that is robust, workable, complete and technically sound; but it must also be moderate, building upon the common ground that has broad acceptance and legitimacy.

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The Scottish Government’s 2014 draft interim constitution was inadequate, because it failed to set out the basic institutional, structural scaffolding that any constitution worthy of the name needs. An equally serious flaw was that it could be amended by ordinary legislation, rendering its guarantees hollow.

Nevertheless, a decent provisional constitution might emerge if the 2014 draft were combined with other sources, such as the SNP’s 2002 draft constitution and the relevant parts (transposed into constitutional form) of the Scotland Act 1998 and other institutional statutes.

Such a provisional constitution would maintain parliamentary democracy with free and fair elections, uphold human rights based on the European Convention and ensure the institutional integrity of the state through an independent judiciary and an impartial civil service.

If – and only if – there is a sufficient consensus, it might go a little further: the SNP’s 2002 draft proposed some socio-economic rights, while the 2014 draft had provisions on climate change, the environment, children’s rights and nuclear disarmament.

What the provisional constitution would not do, however, is try to set itself up as an ideological manifesto, or radically change the system of government. There is a long list of constitutional issues that can be considered, debated and decided, through participatory democratic channels, in the second stage of the process, after independence.

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This includes, but is not limited to: becoming a republic, establishing a new second chamber, changing the parameters of religion-state relations, land reform, and instituting innovative forms of democracy such as sortition, participatory budgeting and citizens’ initiatives.

The way ahead is clear. For now, we must concentrate on developing a complete and resilient, but moderate, provisional constitution on which to build an independent Scotland. Only after independence, with the provisional constitution providing the solid ground on which to stand, will we have the freedom and stability to consider more radical or far-reaching changes.

Dr David Patrick from South Africa is Wednesday’s guest on the TNT show