The Vatican announced yesterday a new legal structure by which Anglicans may enter the Roman Catholic Church. That may sound a pedestrian organisational matter, of interest mainly to canon lawyers. But it is potentially the most explosive development in AnglicanCatholic relations since the Reformation.

Extraordinarily, Dr Rowan Williams, the Archbishop of Canterbury, learnt of the detail only last weekend. The diplomatic nicety of a joint statement between Dr Williams and Vincent Nichols, the Catholic Archbishop of Westminster, cannot obscure a discomforting truth: Dr Williams has been bounced. It is not altogether his fault, but this most learned of primates has been outclassed as a politician.

There are genuine pastoral reasons behind the Holy See’s actions. But the solution and the manner by which it has been derived are a direct challenge to the integrity of the Anglican tradition. Dr Williams has made immense efforts to maintain the unity of the Anglican Communion and advance the ecumenical movement. He has been undermined. He now faces the unenviable prospect of an increasing fragmentation of Anglicanism and a severely attenuated state of Anglican-Catholic relations.

Under a structure known as an apostolic constitution, Anglicans may enter into full communion with Rome while retaining distinctive features of the Anglican liturgical and spiritual tradition. The constitution will establish “personal ordinariates” (similar to dioceses) to provide pastoral care for them. Thousands of Anglicans who are unreconciled to the idea of women bishops and homosexual clergy are likely to respond.

Dr Williams denies that the Holy See’s announcement represents “proselytism or aggression”. It is true that traditionalist Anglicans have been urging the Catholic Church to create a collective space for them. But there are institutions within which discussions between Anglicans and Catholics take place. The Holy See’s Council for Christian Unity played no part in this arrangement. The way it has been sidelined implies that, for Pope Benedict, ecumenism is secondary. His drive for Catholic unity is so intense that it has extended even to welcoming followers of the ultraconservative Archbishop Marcel Lefebvre, among them a bishop who denies the Holocaust. Yesterday’s announcement hinders not only church unity but even church co-operation.

The Pope will arrive in Britain for the first time as pontiff next year. His predecessor, Pope John Paul II, visited Britain in 1982. By any standards an impressive figure, John Paul was at pains to acknowledge his wish for unity and his regard for other Christian traditions. He became the first pontiff to visit Canterbury Cathedral, where he knelt in prayer. In the year before his visit, the Anglican-Roman Catholic International Commission issued a profound report setting out the theological basis on which full communion between the Churches might be advanced.

The auspices for the present Pope’s visit are now less good, and suddenly so owing to yesterday’s announcement. Pope Benedict may preside at the beatification service in Birmingham for Cardinal John Henry Newman, the Victorian divine, who is an important figure in the intellectual and cultural life of the nation as well as of the Church. As the most prominent of all converts to Rome, Newman advised Anglicans that their Church had “left the centre of unity in the 16th century”. Newman’s name is one that could be attached to the new ordinariate for Anglicans. Such disputation was the temper of his times. It should not be the tenor of ours. The Church of England’s witness to the life of the nation is a valued and historic civic resource. Its position has been dangerously weakened.