Mix the flour, yeast, sugar and salt in a mixing bowl. Add the melted butter or oil and gradually mix in the warm water until you have a smooth dough. Knead the dough for 5 minutes on a lightly floured surface until smooth and elastic.
Cut the dough into quarters, then cut each quarter into 10 smaller pieces. Shape each piece into a thin rope about 20 cm (8 inches) long. Bend the rope so that it forms a wide arc, then bring one of the ends round in a loop and secure about halfway along the rope. Do the same with the other end, looping it across the first secured end.
Transfer the pretzels to 2 large greased baking sheets. Cover loosely with lightly oiled clingfilm and leave in a warm place for 30 minutes until well risen.
Make the glaze. Mix the water and salt in a bowl until the salt has dissolved then brush this over the pretzels. Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 6–8 minutes until golden brown. Transfer to a wire rack to cool.
Melt the different chocolates in 3 separate heatproof bowls set over saucepans of gently simmering water. Drizzle random lines of dark chocolate over the pretzels, using a spoon. Leave to harden then repeat with the white and then the milk chocolate.