Pre-heat oven 220c /200c fan/ gas 7 and grease a baking tray.
Place the flour and baking powder into a large bowl, rub in the butter until it resembles fine breadcrumbs and then stir in the finely chopped Fenland celery, 100g of the grated cheese and the chopped walnuts.
Break the egg into a measuring jug, lightly beat and make up to 150ml with the milk, add all but a small amount, reserve to brush the tops with. Mix gently until you have a soft dough.
Knead lightly on a floured surface and roll out to approx. 2 cm thick, cut into 6 cm rounds and place on the baking tray, re roll any trimmings.
Brush the tops with a little of the reserved egg mix and sprinkle with the remaining cheese, bake for 12-15 minutes until well risen and golden. Cool on a wire rack.
Mix together the softened butter and parsley, serve the scones warm, split in half and topped with the butter with the remaining celery to crunch along with.