Mix yeast, sugar and milk in a jug and leave in a warm place until frothy.
Mix flour salt and caster sugar in a bowl, beat in the margarine, eggs and yeast mixture. Mix well and then knead until smooth and elastic.
Place dough in an oiled bag and leave in a warm place until doubled in size. Knead again and roll out 40-50cm square.
Brush with melted margarine, sprinkle with sugar, mixed spice and currants, and roll up. Cut the roll into 16 buns and set on a greased baking tray. Leave to double in size again. When doubled in size bake for 20 minutes at 180C.
To glaze, dissolve the sugar in the milk and water, simmer for 2 minutes, then brush over the hot buns and allow to cool.