How to Sing Classical - Vibrato!

Good vibrations or horrible wobbling? Why do singers use vibrato? Tom Service goes to the wobbling heart of the matter of vibrato in singing. Why does it induce such visceral reactions - love and hate? Is it a matter of classical-singing artifice or is it a welcome and naturally occurring phenomenon in the healthy workings of our vocal cords, in the way our bodies make the sounds we call singing?