Alan Renwick argues that the recent Irish Constitutional Convention offers the best model for pursuing the constitutional change that the UK now urgently needs – one that can rise above sectional interests and engage ordinary voters.

Politicians across the political spectrum now recognise that significant constitutional reforms affecting the governance structures of the UK as a whole are needed. But what form should they take, and how should they be decided on?

The prime minister this morning set out a plan. The West Lothian question will be solved by permitting only English votes for English laws. Demands for the decentralisation of government will be met through the devolution of powers to English cities as well as further devolution to Scotland and Wales. These objectives will be pursued through cross-party talks chaired by William Hague.

Unfortunately, this is an inadequate response to the circumstances we find ourselves in. It is inadequate in terms of both the solutions proposed and the processes that are expected to generate them.

As regards the solutions, the idea of 'English votes for English laws' sounds like a minor, common-sense change. But in fact it has deep and difficult implications. What if, as is quite plausible, the Conservatives win most seats in England at the next election while Labour win most in the UK as a whole? This would require either a grand coalition – which hardly promotes democratic accountability – or, as Conservative MP John Redwood has recognised, separate English and UK governments. But you can't create separate governments on the fly – the delineation of responsibilities, the roles of civil servants, and many other issues would need to be resolved with great care. And if you did manage to create separate governments, the place of the English government within the union would be so dominant as to risk splitting the UK apart in a few years' time – just what the pro-union parties least want.

The only solution to the West Lothian question that makes sense in theory is substantial devolution of powers to regions within England. That way, a reasonably balanced federal system (and some kind of federal system, it needs to be recognised, is inevitable here) could be created. The problem with this option, however, has always been that very few people want English regional government. Most parts of England lack any sense of regional identity. When a limited form of regional devolution was offered to the North East in 2004, 78 per cent of voters rejected it.

The situation is somewhat different now. A movement for 'city regions' has bubbled up over the last year or two. An approach that built on such bottom up engagement – not just in the cities, but also elsewhere – rather than the current standard regions – which were never intended to have more than administrative functions – could gain significant support.

This is where process comes in. The development of proposals through closed talks among senior members of the main Westminster parties over the coming months is inadequate in multiple ways.

First, the proposed timetable is wholly unrealistic. Matters of deep constitutional import need to be decided through careful deliberation, not cobbled together in a few months. The government needs to deliver further Scottish devolution quickly in order to fulfil its campaign pledges. But wider reforms should be allowed to take longer. It is ironic that Conservative backbenchers are those most keen to rush through the most fundamental changes to the structure of the UK for several centuries without due consideration.

Second, a closed discussion within a committee of MPs is no place to work out major constitutional changes. We have just seen the highest turnout in any vote in the UK's democratic history. Many Yes voters – who, we should remember, number not far short of half the Scottish electorate – were motivated to turn out in significant part by a belief that democratic renewal could happen through independence. Scots have thus manifested a desire to take part in a process of democratic renewal. Beyond Scotland, support for UKIP is a symptom of a much broader exasperation with the political elite. Douglas Carswell – champion of participatory democracy – looks set to win a by-election for UKIP in a few weeks' time. Against this backdrop, it looks remarkably tin-eared and out-of-touch to propose a reform procedure that is so elitist and exclusive.

Third, whatever the immediate politics of the issue, we now have a wealth of evidence that suggests that such closed, elite-driven procedures are not in general the best way to design a constitution. In April, I published a pamphlet with the Constitution Society that examined options for a constitutional reform process. Negotiations among leaders, I argued, would tend only to entrench those leaders' interests rather than promote the well-being of all and their proposals could fail to secure public legitimacy.

Fourth, many of the issues that a constitutional reform process will need to decide upon are ones upon which ordinary citizens are the experts. Whether the people of, say, Cornwall will, after due deliberation, want a degree of autonomy is something that only the people of Cornwall can judge. (The phrase 'after due deliberation' is important here. Ordinary citizens need to be engaged actively; merely asking survey questions is not enough on issues such as these.)

For all these reasons, trying to negotiate the terms of the UK's federalisation among the narrow political elite will not do. A much more open approach is need. Ed Miliband has recognised this in his statement this afternoon, calling for a slower, more consultative process, including a constitutional convention that will consider the range of options carefully. Even here, however, there is much devil in the detail. What form should such a constitutional convention take?

A number of such approaches are available: I examine four serious runners in my pamphlet. One of these – a civil society convention on the model of the Scottish Constitutional Convention that operated between 1989 and 1995 – has many supporters: the precedent is one that many who remember the Convention like. But a civil society convention can never properly represent the whole of society, and the question of who should be in and who should be out has no clear answers.

In fact, I argue that another option – the model of the recent Irish Constitutional – is the best. The Irish Convention comprised 100 members: 33 politicians chosen by the parties, 66 ordinary citizens randomly chosen from the electoral register, and an independent chair chosen by the government. It deliberated over a series of aspects of the Irish constitution across a number of weekends, in each case hearing expert accounts of the issues at stake, speaking with members of relevant pressure groups, deliberating among themselves with the support of trained facilitators, and finally making decisions.

Concerns were expressed at the Convention's inception that its mixed composition would not work: that the politicians would dominate and the ordinary citizens' voice would not be heard. That is not what happened. Detailed research by Jane Suiter and colleagues shows that members of all types overwhelmingly felt able to express themselves. The Convention members deliberated well and produced clear, reasoned conclusions. Those conclusions are now being taken forward: the government has already promised three referendums for 2015 based on the Convention's recommendations, and more may follow.

Thus, a convention of this form can reason about reform options at a high level. It can avoid control by party interests. It can engage ordinary voters at the heart of democratic reform debates. It can carry considerable public legitimacy. It can also engage politicians – something that pure citizens' assemblies have struggled to do – thereby increasing the chances that its proposals will in fact be enacted. Its application in the UK would require changes to some details, but the basic model is clear.

If the UK's politicians want genuinely to respond to public disillusionment over the state of our democracy and work out an answer to the West Lothian question that will work in practice as well as theory, following something like the Irish model is the best approach. By contrast, if they take the path set out by David Cameron today, they risk further alienating the public and rushing into a constitutional quick-fix that will not work and will threaten the stability of the union over the long term.