Grease 2 baking sheets.
Mix together the raisins, spice and sugar. Roll out the pastry on a lightly floured surface to a 30 x 20 cm (12 x 8 inch) rectangle. Mix the egg yolk with the measurement water and brush some of it sparingly over the pastry, taking it right to the edges. Sprinkle with the raisin mixture. Roll up the pastry, starting from a long side, to shape a neat log. Wrap in clingfilm and freeze for 30 minutes.
Trim off the ends from the pastry log. Using a sharp knife, cut across into 22 slices, 1 cm (½ inch) wide. Roll lightly with a floured rolling pin to flatten slightly, then transfer to the baking sheets. Brush with the remaining egg yolk.
Bake in a preheated oven, 220°C (425°F), Gas Mark 7, for about 12 minutes until risen and golden. Serve warm or, if preferred, transfer to a wire rack and leave to cool a little or completely.
Drizzle with a little sherry to serve.