Wipe the apples and leave on the peel if it is a pretty red colour. Quarter and core the apples and cut into neat dice. Shred the celery and coarsely chop the walnuts.
Mix together the mayonnaise and lightly whipped cream to make a very light dressing and sharpen with a squeeze of lemon juice. Combine at once with the prepared apples to prevent discolouration of the apple pieces. Mix in the shredded celery and leave in a cool place until ready to serve. Just before serving, mix in the coarsely chopped walnuts.