PETULA CLARK will be starring this week in The Song's the Thing in the Light Programme and also, of course, in her own show in television on Tuesday. Petula--she doesn't respond very favourably to being called Pet--is a remarkable young lady. At twenty-three she is already a veteran of show business, having first appeared on the stage at the age of seven, and sung at the Royal Albert Hall at the age of ten. Since then she has appeared in twenty-four films, broadcast in innumerable radio and television shows, made a great many records, and is still neverthless something of an ingenue. 'I hate being called that,' she said, 'but I suppose it's true.' Any doubts we might have had were displled when we asked her about the colour of her hair. 'You could call it Titian,' she said, 'but really it's just toffee-coloured.'