Preheat the oven to 220ºC, gas mark 7. Stir together the flour and baking powder. Then, using your fingertips, rub in the butter until it resembles breadcrumbs. Using a table knife, stir in three quarters of the cheddar and then the milk to make a fairly soft dough.
On a lightly floured surface, pat the dough out to a thickness of 2cm and stamp out 5cm wide rounds. Reuse the trimmings to make a total of 12 scones. Transfer to a non-stick baking sheet, brush lightly with milk and scatter over the reserved cheese. Bake for 10-12 minutes until risen and golden brown. Transfer to a wire rack and leave to cool.
Split each scone in half, spread the base with soft cheese, top with a piece of smoked salmon and sprinkle over some cress before replacing the top. Serve with small wedges of lemon for squeezing over the salmon.