Sieve the flour, salt, baking powder and mustard powder into a bowl. Rub in the margarine until the mixture resembles fine breadcrumbs.
Stir in the grated Sheese, and add enough water to create a smooth dough.
Roll the dough out on a lightly floured surface to a thickness of about 4-5cm. Then cut into rounds with a cutter, or roll the dough into a circle and cut into wedges. Decorate the tops of scones with sesame seeds or the seeds of your choice.
Bake at 220 °C for 10-15mins or until the scones are golden brown.