Preheat the oven to 200°C/fan 180°C/gas mark 6. Put the flour in a large bowl, add the butter and rub it into the flour with your fingertips. Stir in the sugar, sultanas, chocolate chips and mixed spice.
In a jug, beat together the egg and milk. Pour into the flour mixture and bring together to make a soft dough.
Dust a work surface with the extra flour and roll out the dough to 2cm thick. Using a 5cm cutter, stamp out the scones and put onto a baking tray lined with baking parchment. Reroll the trimmings and stamp out more rounds to make 10 scones.
To make the crosses, mix together the plain flour with 1 tbsp water and knead to make a smooth dough. Roll out thinly, then cut into strips. Lay the strips on top of the scones to make crosses. Brush with the extra milk, then bake in the oven for 15 minutes until golden.
Mix together the caster sugar with 1 tbsp water and use to glaze the tops of the scones as they come out of the oven. Cool on a wire rack and split to serve.