I was once chatting with a group of senior Church of England clergy when an elderly priest passed by. He was a devout Anglo-Catholic – more Catholic than the Pope, some said – and loved and revered for his holiness by all who knew him. “The trouble with him,” remarked one of my companions as we watched him walk away, “is that he doubts the validity of his own orders.”

I’ve no idea how many priests there are in the Church of England haunted by the same uncertainty. It struck me how cruel Christianity can be to its own most faithful servants. That Anglican priest’s doubts flowed directly from a ruling issued in 1896 by Pope Leo XIII, which stated that Anglican orders were “absolutely null and utterly void”. It meant that Anglican ordination was a meaningless gesture, and that those thus ordained remained mere laymen.

Pope Leo’s decree Apostolicae Curae was a slamming of the door that continues to reverberate, an apparently insuperable obstacle to greater unity between the Catholic Church and the Anglican Communion. It is the reason why Anglican priests who become Catholic priests still have to be reordained, albeit conditionally (i.e. “if not already a priest”).