Tony Blair’s conversion to Catholicism has opened a can of worms.

The only surprise about Tony Blair’s reception into the Catholic Church on Friday was that it took him so long. His wife Cherie is a cradle Catholic and throughout the 10 years that he was prime minister, Mr. Blair attended Sunday Mass, with or without his family, wherever he was in the world.

He was mildly rebuked by the late Cardinal Hume for receiving communion in Catholic churches while still an Anglican, but he did not seem very contrite. Before the court of his conscience he was innocent, for, like many other Anglicans and Episcopalians, he had always considered himself a member of the “one, holy, catholic and apostolic church” which both Catholics and Protestants invoke in the Nicene Creed.

The news of Mr. Blair’s conversion was greeted with howls of dismay from some Catholics, who demanded a grovelling apology from him for having been on the wrong side of so many moral issues, from abortion, euthanasia, and embryonic stem cell research to Sunday trading. The Conservative politician Anne Widdecombe fulminated that unless Mr. Blair publicly repudiated his previous views, “it will seem as if the Church did make an exception for somebody just because of who he is.”

One pro-life campaigner likened Mr. Blair’s conversion to a vegetarian joining a meat eater’s club.

But a church is not a club. If Mr. Blair was able to satisfy not only the priest who had been preparing him, but Pope Benedict himself that he was ready to become a Catholic, it is not for self-appointed defenders of the faith to object. Ms. Widdecombe — who until Mr. Blair came along was herself the most high-profile recent Catholic convert in Britain — has reinforced the worst anti-Catholic stereotypes. She really does seem to think that she is more Catholic than the Pope.

Does it matter that Mr. Blair has become a Catholic? For non-Catholics, no — but his conversion is a reminder that there is a great deal of unfinished constitutional business left over from the past. The religious conflicts of the Reformation, the Civil War, and the Glorious Revolution were never resolved, merely shelved until the passage of time took the heat out of them.

The Act of Settlement of 1701, still in force today, not only prohibits Catholics from inheriting the throne or marrying a monarch, but absolves Britons of their allegiance to any Catholic who exercises “regal authority, power or jurisdiction.” This used to be taken to mean that those who exercise the powers of government also could not be Catholics. Whether or not that is the law, there has never been a Catholic prime minister. It was partly for this reason that Mr. Blair hesitated to undergo formal conversion while he was still in office.

To abolish the Act of Settlement, as the Catholic Church regularly demands, would necessitate a full-scale reform. For the exclusion of Catholics from the throne is no more contrary to human rights than the royal succession, which privileges male heirs over female ones. Modernizing the monarchy risks also upsetting the precarious balance of the Commonwealth countries in which the Queen is still head of state, such as Canada and Australia. They might take the opportunity to declare themselves republics. The consequence might be a revival of separatism in, for example, Quebec.

But it is upon the Church of England that reform would have the biggest impact. Though Britain is anything but a theocracy, the same person is head of both church and state. On the day after Mr. Blair’s conversion, it emerged that fewer worshippers attend Anglican churches than Catholic ones. So it is getting harder to justify the establishment of the Church of England on purely numerical grounds.

In fact, the only defense of the established church that I have read lately came not from an Anglican, but from the chief rabbi, Sir Jonathan Sacks. His view is that the status quo is in the interests of minority faiths, such as Jews, because it avoids disputes over primacy: the established church is primus inter pares, first among equals, and that is that.

The trouble is that this same church wastes no opportunity to undermine the faith that sustains it. This Christmas, the archbishop of Canterbury, Rowan Williams, took it upon himself to explain that the three wise men and many other aspects of the nativity story were mere “legend.” At about the same time, Pope Benedict was elucidating the meaning of the Epiphany, the adoration of the Magi, as the revelation of a personal God who “governs the stars … We are not slaves of the universe and of its laws, we are free … Heaven is not empty.”

Did Mr. Williams, who is an Oxford theologian, think that by jettisoning such baggage, he was making the task of resisting the atheists, led by Richard Dawkins and Christopher Hitchens, easier? If so, he need only ask himself why Tony Blair felt that he had to leave the Church of England to see that he is playing the atheists’ game.

Instead of explaining the stories from which religion derives its ability to sustain people through catastrophe and suffering, the Archbishop explains them away. Christianity, like Judaism, is so saturated with these meta-narratives that it is incomprehensible without them.

Atheism has no narrative at all. If the Church of England, or any other form of Christianity, tries to flatter the secular world by imitating it, its believers will — like Tony Blair — vote with their feet.