Preheat the oven to 200°C, fan oven 180°C, Gas Mark 6. Put a baking sheet into the oven to preheat. Sift the flour and salt into a large mixing bowl and rub in the butter, using your fingertips, until the mixture looks like fine breadcrumbs. Stir in the sugar, lemon zest and South African raisins.
Beat the egg in a measuring jug, then add milk to bring the liquid up to 300ml, mixing well. Add just enough of this to the rubbed-in mixture to make a soft (not sticky) dough - there will be a little liquid left. Bring the mixture together with a round-bladed knife.
Turn the dough onto a lightly floured surface and knead lightly for a few moments. Roll out to about 3cm thick – it’s a mistake to roll the dough more thinly! Use a 5cm plain or fluted cutter to stamp out rounds. Avoid twisting the cutter - just press it straight through to help the scones rise evenly. Gather any trimmings, re-roll and cut out more scones.
Arrange the scones quickly onto the preheated baking sheet. Brush the tops with the remaining egg mixture. Immediately transfer to the oven and bake for 15-18min towards the top of the oven, until well-risen and golden brown. Cool for a few moments, then transfer to a wire cooling rack. Serve warm with lemon curd and clotted cream.