Pre-heat the oven to 160°C/325°F/gas 3.
Lightly grease two baking trays. Measure the sugar and margarine into a bowl and cream together. Add the oats and flour and work into the mixture. Lightly knead the mixture until smooth and roll out to a thickness of ¼” (5mm) on a lightly floured surface. Cut into rounds using a 2½” (6cm) cutter and place on prepared baking trays. Bake in the oven for 20 minutes, or beginning to colour. Lift onto a wire rack to cool.
Using margarine rather than butter results in a more shortbread-like product.