Unworldliness is the most charitable defence of the Archbishop of Canterbury's suggestion that introducing some aspects of sharia law in Britain is "unavoidable". Dr Rowan Williams is a theological scholar with an admirable record of reaching out to find common ground with the sincerely- held beliefs of people of faiths other than Christianity. His study of religious history should have forewarned him that mixing religion and politics is a surefire recipe for division. His case for the recognition of sharia law in Muslim communities in Britain is essentially one of recognition for religious belief. The case against is that two parallel sets of laws are not only unworkable, but completely at odds with the basic principle that the law applies to everybody equally. In conflating religion and the laws of the state, he has managed to polarise opinion in a debate in which he had sought consensus.

Informal sharia courts already operate in some Muslim communities in England, where they rule on issues such as divorce and financial disputes. Where this operates to both parties' mutual satisfaction, the participants abide by the decisions voluntarily, but, in the long term, decisions that have no legal standing cannot be satisfactory. There are cases of confusion where people believe they are married or divorced when that is not the case in law. In seeking "a constructive accommodation with some aspects of Muslim law", Dr Williams is perilously close to failing to see that too much of its practice operates to the detriment of women and children. It has taken a long time to enshrine equal rights for all in UK law and, as the European Court of Human Rights ruled in 2001, sharia law is not compatible with the European Convention on Human Rights.

While Dr Williams was advocating no more than that sharia courts could be recognised in civil disputes, divorces could include allegations of adultery, which in some countries carries the death penalty and prevents women reporting rape. Dr Williams's proposal, that Muslims should not have to choose between the "stark alternatives of cultural loyalty and state loyalty", may have been intended as an olive branch following the controversial remarks of the Bishop of Rochester, Dr Michael Nazir-Ali, that some communities in England are "no-go areas for non-Muslims", but, in effect, it reinforced that notion of division by suggesting that Muslims could choose which set of rules to live by.

The word sharia, meaning the path to a watering hole, however, can be understood as a code for living rather than a system of law. In that sense, it is possible to make financial transactions, for example, compatible with sharia principles without undermining civil liberties. The need to live harmoniously in a multicultural society has sometimes been woefully misinterpreted as requiring differences to be avoided rather than celebrated. It is time to reverse that and a properly and positively pluralist society is one that allows different cultures and faiths to flourish, but none can do so unless based on the fundamental principle that one law applies equally to all.