22/09/2014 07:41 BST | Updated 19/11/2014 05:59 GMT

The Mathematics of Devolution

Whatever one might think politically, the Scottish "No" vote avoids some nasty questions for those of us who live south of the border. Would we have found a new home for Trident? Would the reduction of clout have prevented us reforming the EU? Would it have lost us our seat on the Security Council? How would the debt be divided - and indeed the oil? No-one can be sorry to see the files on those topics hit the bottom of the waste paper basket. Still there are a couple of questions left to stretch our patience over the coming months.

The first - exactly which areas of policy should be devolved-is essentially political and can be hammered out by the politicians with their usual mix of bombast and compromise. The areas devolved will no doubt change over the years, so boundaries can be adjusted later. Far more difficult is the technical question of how devolution will work mechanically, in a way which answers the West Lothian question by letting English voters rule on English issues, without multiplying costs.

Assuming that there is no appetite for spending money on a separate English parliament, the House of Commons in one form or another is going to have to fill a role in relation to England equivalent to that of the Scottish Parliament and the Northern Irish and Welsh Assemblies. At the simplest level that can be done quite easily. Suppose that a topic is devolved to the three regional assemblies, then English legislation on that topic should be enacted by the English MPs. What then if it is only devolved in Scotland and Wales? The answer must be that Scots and Welsh MPs are excluded, so that the English and Northern Irish MPs decide for the rest of the UK.

Now suppose that an issue is of particular interest to England but unimportant to the rest of the UK. One might want to devolve it to an English assembly but leave the legislation for the rest of the UK to the House of Commons. Clearly English MPs would be excluded from the House's deliberations for the legislation affecting Scotland, Wales and Northern Ireland but where is the assembly to which the English legislation is to be devolved? If one had an English assembly the answer would be obvious but, failing that, one is thrown back to the group of English MPs. In other words, the English MPs acting together would function both as a low cost English assembly and as all or part of the residual legislature where an area has been devolved elsewhere.

One effect of the devolution debate is a call for powers to be devolved to other parts of England such as London or Cornwall. The system is flexible enough to accommodate that. Suppose the planning rules are to be different in London from the rest of the UK. Then the London rules could be devolved to the Mayor, with London MPs being excluded from the debate on the general legislation. If there was devolution to Birmingham as well, MPs from London and Birmingham could be excluded.

No doubt all this can be made to work but the change to the governance of the UK would be profound as would the way in which political parties think and function. One can easily imagine Labour celebrating an election victory in 2015 but the Tories taking the consolation prize of controlling England's group of MPs. Then whether an issue was decided for England on Labour or Conservative lines would depend on whether it had been devolved in Scotland or Wales - a temptation to chicanery if the question of whether to devolve lay with the Government of the day.

Major constitutional reforms are highly vulnerable to the law of unintended consequences and it is going to require the wisdom of Solomon to get all this right. Unfortunately Solomon is not available to us at the moment and there isn't much time to work it all out either.

When the transport authorities design road systems they call in mathematicians not politicians and designing a new political system is rather similar. This project really must not be left to amateurs to develop and the sooner that a group of mathematicians, political scientists and experts on parliamentary procedures is put together to analyse the options and explain them to parliament and the public, the better will be the solution.