What has happened? Pope Benedict XVI has approved an apostolic constitution, or decree, under which traditionalist Anglicans dismayed by women priests and bishops will be given “personal ordinariates”. These will allow Anglicans to enter into full communion with the Catholic Church while preserving elements of their Anglican identity.

What does it mean? It is a severe blow to hopes for a negotiated Anglican-Roman Catholic unity settlement and a setback to Dr Williams’s attempts to maintain the unity of the Anglican Communion. The Archbishop did not see this coming, in spite of well-publicised pleas to Rome for help by leaders of traditional Anglican groups. The deal was done by the Congregation for the Doctrine of the Faith and not the body responsible for ecumenism, the Council for Christian Unity. It thus undercuts decades of dialogue.

What happens next? Cardinals in Rome will flesh out the detail of the new Anglican ordinariates. The Pope will visit Britain next September, when he could choose to link the new structures to the Church of England’s most noted convert to Rome, Cardinal John Henry Newman, due to be beatified next year. Meanwhile, the Church of England will recapture the moral high ground in the eyes of the secular, English-speaking world by consecrating women bishops. It might even liberalise its position on homosexuality.

What Catholic beliefs must defecting Anglicans embrace?

These are set out in the Catechism.

- Jesus prayed that his followers should be one. Catholics believe Christian unity under the authority of the Pope to be an imperative. He is infallible when “he proclaims by a definitive act a doctrine pertaining to faith or morals”.

- Women can never be ordained to the priesthood. Only a baptised man can validly receive ordination.

- Mary, the mother of Jesus, was conceived “immaculately”, which means she was protected from sin from birth.

- Homosexual acts are “contrary to the natural law . . . under no circumstances can they be approved”.

- Transubstantiation, or the doctrine that the bread and wine actually become the body and blood of Christ.