Peter Singer arrives for lunch with the liberated air of an east coast intellectual taking a break from George Bush’s America. The other diners at Woodlands, a Tamil vegetarian restaurant near Piccadilly Circus, don’t look up as he and his wife, Renata, pass by. Doubtless none of them realise that the lightly tanned man with wisps of white hair is one of the most consequential thinkers of our time: a radical philosopher whom many regard as the father of the animal liberation movement. The restaurant was my choice, not his. Singer asked me to book an old vegetarian haunt called...