Sift the flours and salt into a warm bowl. Cream the yeast with the sugar. Add the warmed water, then the oil. Stir into the flour to make a batter, and beat vigorously until smooth and elastic. Cover the bowl, put in a warm place and leave it until the mixture rises and the surface is full of bubbles (about 1 1/2 hours). Break it down by beating with a wooden spoon. Cover and leave in a warm place to prove for another 30 minutes. To cook the crumpets, heat and grease the bakestone lightly. Grease 5 or 6 crumpet rings (3-3 1/2 inches) (or scone cutters) and put them on the bakestone to heat. Cook as many crumpets as possible at a time, as the batter will not stay bubbly for long. Put 1/2 inch deep of batter into each ring. Cook gently for 7 - 10 minutes, or until the surface sets and is full of tiny bubbles. Using an oven glove for protection, lift off the ring, and if the base of the crumpet is pale gold, flip it over and cook for another 3 minutes until the other side is just colored. If the crumpet batter is set but sticks slightly in the ring, push it out gently with the back of a wooden spoon. Wipe, grease and heat the rings for each batch of crumpets. If serving immediately, wrap the crumpets in a cloth and keep warm between batches. Butter generously and serve at once. If reheating, toast the crumpets under the grill, cooking the smooth surface first and then the top so that the butter will melt into the holes.