Grease and flour a 26cm cake tin. In a medium bowl, cream together the butter, margarine, sugar and vanilla essence. Beat in the eggs, one at a time. Then stir in the evaporated milk. Combine the salt and 300g of flour, stir into the wet mixture. Toss the remaining flour with the walnuts, add to the batter and mix well. Finally, fold in the cherries. Pour the batter into the prepared tin.
Place cake into a cold oven, then heat to 150 C / Gas 2. Bake for 2 1/2 hours. Cool for 15 minutes in the tin before inverting onto a plate to cool completely.