Spirituality is a common term these days, used by Prince Charles, and by the Archbishop of York as a way of stepping beyond religious divides.

But many now call themselves "spiritual" but not religious. About a fifth of people in the UK fit into this category, according to Prof Michael King from University College London.

In the US, a Newsweek survey in 2005 put the figure at a quarter. A survey in October by the Pew Research Center suggested a lower figure with a fifth of people religiously unaffiliated and 37% of those regarding themselves as spiritual but not religious.

King's research suggested that in the UK the "spiritual" group are more likely to have mental health problems, such as anxiety or depression.

There will be people who will dispute the research, but it's certainly clear that the "spiritual, but not religious" represents a major strand of belief across the West.

It's a broad church, so to speak. The spiritually aligned range from pagans to devotees of healing crystals, among many other sub-groups.

But for millions of others it is nothing so esoteric. Instead, it's simply a "feeling" that there must be something else.