In 1971, the English composer Gavin Bryars was working "on a film about people living rough in the area around Elephant and Castle and Waterloo Station."

In the course of being filmed, some people broke into drunken song - sometimes bits of opera, sometimes sentimental ballads - and one, who in fact did not drink, sang a religious song "Jesus' Blood Never Failed Me Yet."

When I played it at home, I found that his singing was in tune with my piano, and I improvised a simple accompaniment. I noticed, too, that the first section of the song - 13 bars in length - formed an effective loop which repeated in a slightly unpredictable way. I took the tape loop to Leicester, where I was working in the Fine Art Department, and copied the loop onto a continuous reel of tape, thinking about perhaps adding an orchestrated accompaniment to this. The door of the recording room opened on to one of the large painting studios and I left the tape copying, with the door open, while I went to have a cup of coffee. When I came back I found the normally lively room unnaturally subdued. People were moving about much more slowly than usual and a few were sitting alone, quietly weeping.

I was puzzled until I realised that the tape was still playing and that they had been overcome by the old man's singing. This convinced me of the emotional power of the music and of the possibilities offered by adding a simple, though gradually evolving, orchestral accompaniment that respected the tramp's nobility and simple faith. Although he died before he could hear what I had done with his singing, the piece remains as an eloquent, but understated testimony to his spirit and optimism.

I know how Bryars' colleagues felt. I think that I'm still crying from the other night. If there is one album you must hear, it's Jesus' Blood Has Never Failed Me Yet. Featuring the Hampton String Quartet and Tom Waits, "Jesus' Blood," as conservative blogger Orrin Judd wrote in his Amazon review, leaves the "the listener cleansed, healed and profoundly moved."

You would think that a 74-minute loop of the same 13 bars would be annoying or at least monotonous but it's not. Then again, to paraphrase Renee Zellweger in Jerry Maguire, they had me at the title.

    Jesus' blood never failed me yet
    Never failed me yet
    Jesus' blood never failed me yet
    This one thing I know
    That he loves me so ...