The Vatican has mounted a direct challenge to the unity of the Anglican Communion. It established last month a new legal structure by which Anglicans may enter the Catholic Church. Traditionalist Anglicans, for whom the arrangement was designed, were delighted. But Dr Rowan Williams, the Archbishop of Canterbury, was treated unconscionably in the process. Dr Williams will meet Pope Benedict tomorrow in Rome. In the interests of his own authority and the integrity of the Anglican tradition, he should give the pontiff two clear messages.

First, the Anglican Communion is not an arrangement of convenience among disparate parties. In creating the new structure, known as an apostolic constitution, the Vatican acted precipitately. Second, there is an impeccable case for the Church to welcome women priests and homosexual clergy. On these issues that have sharply divided Anglicans, Dr Williams is clearly liberal by temperament. Stating that position openly, regardless of its effect on Anglican-Catholic relations, is overdue.

Relations between Canterbury and Rome are shaped by shared history and doctrine. Some years before his conversion to Catholicism, John Henry Newman, the Victorian divine, wrote a seminal exposition of Anglicanism in his Prophetical Office of the Church. He maintained that the essential points of the Church of England were its dogma, its sacramental system and its legitimate claim to be a “Catholic” Church.

That notion of the essential unity of Anglicanism and Catholicism on doctrinal fundamentals exercised a strong hold till recently. The Church of England has pursued ecumenism with other churches, notably in an abortive effort at unity with Methodism in the 1970s. But reunion with Rome became a dominant concern for the Church of England after the Second Vatican Council in the 1960s.

The liberalising effects of the council, called by the great reformist Pope John XXIII, included a greater openness to other Christian traditions. There followed a succession of joint Anglican-Catholic statements on doctrine and authority. The unilateral decisions of the present papacy are an affront to that patient work.

Dr Williams puts the best face that he can on the state of Anglican-Catholic relations. Speaking at a conference this week, he noted that decades of dialogue had achieved wide consensus on the Churches’ common theological heritage. But the Vatican’s announcement last month, with only the barest of notice given to Dr Williams, of the new apostolic constitution was not about doctrinal niceties. It was raw politics. A man of deep faith and wide learning, Dr Williams was outclassed when it came to baser arts.

Today’s meeting should be the occasion for a tougher tone. The Vatican has driven a wedge into the Anglican Communion. The Pope’s decision has undermined Dr Williams’s authority. Dr Williams has made valiant attempts to keep Anglicans united, partly for the sake of relations with Rome. He should recognise when effort is unavailing. There is every good reason, in theology and natural justice, for the Church to embrace the ministry of women and homosexuals. Anglicanism will be richer for it. Dr Williams will be a bigger man for espousing it unreservedly.