The story began last year when my wife, who is 38, gave birth to her second and my fourth child (I have two grown-up daughters from my first marriage). At the age of 52 I thought I had probably done my bit for the world's population, and my wife was sure she had done hers, which left the tricky question: what do we do about contraception? Having rejected the other options we talked about me having "the snip", a word cleverly designed to make the procedure sound as easy as cutting hair or clipping nails.