As we all know, it’s safe for three people to sing hymns in church, but any more than three is absolutely deadly. Those are the rules as set down by the Church of England, and as a result no one in Anglican services (or Catholic ones) will hear the glorious Good Friday Hymn 'O Sacred Head’ tomorrow in the four-part harmony it requires.

But if you stick on a CD of Bach’s St Matthew Passion, you'll hear four separate harmonisations of perhaps the most haunting hymn tune ever written. The Cantor of St Thomas’s Leipzig was obsessed with this tune, originally a popular song with excruciating lyrics by the composer Hans Leo Hassler. Bach’s older contemporary Dietrich Buxtehude had fun with it, as did Paul Simon – enchantingly, in his 1974 song ‘America’. 

This episode of Holy Smoke tells the story of the piece, and reveals some of the miraculous things Bach did with it in his other settings. He has a way of dive-bombing a movement with it that can make you jump out of your seat the first time you hear it. Or, in the case of its guest appearance in the Christmas Oratorio, dance round the room. 

I hope you enjoy this episode. But be warned: you’ll also hear the podcast host attempting to perform one of Bach’s chorale preludes on the piano in his bedroom. Fortunately it only lasts two minutes, so you just have time to nip out and make a cup of tea.