The so-called British constitution has always been a mess.

In the sense in which the word constitution is used from Poland to Portugal and from Nova Scotia to New South Wales – as a fundamental basic law that regulates the powers and institutions of the state – it does not even exist.

Fearful of the democratising potential of a constitution that would protect our rights and hold rulers to a higher law, the British establishment has preferred to rely on the untrammelled power of a sovereign (but well-whipped) Parliament, a motley collection of statutes cobbled together over the centuries, some hallowed traditions made up on the fly, and a set of unwritten conventions that can be rehashed, recycled, and twisted beyond recognition to suit the needs of the Government of the day.

For all this, it works. It works exactly as a game of football would work if the team in possession could appoint the referee and make up the rules as they go along (but the team strip would, for form's stake, remain unchanged throughout the centuries). It works for winners and those already at the top. For ordinary citizens, especially those far from the centres of power, not so much. The electoral system for the House of Commons is unrepresentative, the composition of the House of Lords is indefensible, the powers of the Crown are excessive, secretive and unaccountable, rights are fragile, and privileges rife.

The half-hearted constitutional reforms undertaken by Tony Blair's Government – the removal of (most) hereditary peers, devolution, Freedom of Information, the Human Rights Act, the establishment of the UK Supreme Court – have not fixed the underlying problem of parliamentary sovereignty. The parliamentary majority can still change the rules at will – enabling the Tories to threaten to opt out of the Human Rights Act or amend the Freedom of Information Act to keep the actions of the Queen and the Prince of Wales hidden from the public eye. This is what always happens without clear and enforceable constitutional ground rules: those in power make up the rules to suit themselves as they go along.

If anything, by breaking the old certainties, changes since 1997 have only compounded the problem into one of constitutional dysfunction, where we do not even know what the canons are any more. On the one hand, by the orthodox doctrine of the British constitution, the Scottish Parliament is a simple creature of Westminster statute, and can be abolished or deprived of its powers at will, just as the devolved Stormont Parliament was abolished in the 1970s.

On the other hand, some maintain that the Scotland Act is politically entrenched and its abolition would be deemed unconstitutional (except, of course, when the UK Government says it isn't, and decides to do it anyway, no doubt pleading some great necessity). If anyone thinks this sounds ludicrous, remember the current Scottish Parliament sits for a five-year term, rather than the usual four years, because the UK Fixed Term Parliaments Act 2011 changed it, for convenience's sake, so as not to clash with the more important elections to the real Parliament at Westminster.

The latest example of Westminster's constitutional jerry-building was announced this week. In a bid to solve the notorious West Lothian problem (the fact that Scottish, Welsh and Northern Irish MPs can vote on English legislation, but English MPs cannot vote on Scottish, Welsh or Northern Irish legislation), it has been proposed that a change to the internal rules of the House of Commons would create a new fourth reading stage for England-only legislation, at which only English MPs should be allowed to vote. On current voting patterns, this gives English Tories a veto over the legislative agenda of any future Labour UK Government in as far as that agenda relates to England.

It would mean a Labour UK Minister for Education, having responsibility for education policy in England, would not be able to legislate without the consent of the English Tory MPs. The same situation would be replicated across the departments.

The only way to avoid obstructionism would be for the Labour Government to appoint Tory ministers for English affairs, and for these ministers to become an English Tory Government within a semi-detached UK. Is this not the situation Labour opponents of independence, out of solidarity for our suffering friends and brethren to the south, insist we must vote No to avoid? The argument that the UK protects England from the Tories, always shaky at best, has vanished.

These constitutional issues ought to be central to the independence debate. Aside from the intrinsic advantages of improving the quality and resilience of democracy, all the economic promises of independence depend on good governance: having a system of government that serves the common weal, and not one that serves only the private interests of a few.

There is a direct connection between allowing rulers to make up the rules as they go along and the failure of the UK state to serve the common good. The banking crisis, the expenses scandal, phone hacking, illegal surveillance, persistent unemployment and wage cuts, rising inequality, corporate lobbying, and the destruction of public infrastructure and services – all point to a state that has fallen into the hands of an unchecked oligarchy, bound by its own self-interest.

An independent Scotland offers the chance to do things differently. The best case for independence does not rest primarily on nationalism, nor economic arguments, but upon good governance and democracy: the belief that a Scottish state could do a better job of serving the common weal than the UK has done. Independence is, at root, the re-constitution of Scotland: it forces us to consider how we might be better governed – not just who should govern, but how to improve the system and the ground rules of government, and to how to articulate the principles and values on which all government ought to be based.

In this respect the SNP has been a pioneer. The party's draft constitution for an independent Scotland, published in 2002, provides an example of how a modern, democratic Scotland could be constituted – in a way that protects the rights of citizens and ensures an inclusive parliamentary democracy based on proportional representation. The constitution could be amended only by a three-fifths majority in Parliament followed by a referendum, thereby upholding the sovereignty of the people against the will of the Government of the day.

This 2002 draft is unlikely to be the final constitution of Scotland. Short and generic, it omits some of the advanced provisions many would wish to include. Nevertheless, it shows what independence can achieve: a constitution every bit as good as those of our Scandinavian neighbours, and a state that belongs to the whole community, not to the politicians or party in power.

The Scottish Government has committed itself to an inclusive constitution-making process after independence. That is right and proper, but it could take years of negotiation, during which there is a risk of constitutional deadlock.

The priority is to prepare a robust interim constitution, ready to go from independence day. Only this can guarantee democratic principles and fundamental rights until the constitution is approved. A detailed commitment in the White Paper would do much to distinguish Scotland's democratic principles from Westminster's shoddy expediency.

Dr W Elliot Bulmer is research director of the Constitutional Commission. His book, A Model Constitution for Scotland: Making Democracy Work in an Independent State, is available from Luath Press, £9.99.

Ian Bell is away.