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There was a time when religion was a public matter in England. Queen Victoria was very much in favour of faith, seeing it as a force for good, uplifting the downtrodden and helping correct human imperfection. One of her prime ministers – Lord Melbourne – was of a different cast of mind. An unreconstructed roué, Lord Melbourne is reputed to have said, after walking out of a church service following a sermon that offended his sensibility by speaking ill of adultery: “Things have come to a pretty pass when religion is allowed to interfere with private life.”

Lord Melbourne may well have been prescient. Certainly, contemporary England has nicely put religion in its place: on the margins.

It is not that the...