Make the pastry: sift the flour and a pinch of salt into a bowl. Add the margarine and rub it into the flour with your fingertips until the mixture resembles fine crumbs.

Mix in the grated cheese and just

enough cold water to draw the mixture together to a firm dough. Wrap in cling film and refrigerate for 30 minutes.

Heat the oven to 180C/350F/Gas 4. Meanwhile, make the filling: cook the potatoes and carrots in boiling salted water for 10 minutes. Drain thoroughly, then place in an 850 ml (1 1/2 pint) pie dish with the leeks, mixing them well together. Sprinkle with the parsley and salt and pepper to taste. Set aside.

Melt the margarine in a clean saucepan, sprinkle in the flour and stir over low heat for 1 - 2 minutes until straw-coloured. Gradually stir in the stock, then bring to the boil and simmer, stirring, until thick and smooth. Pour over the vegetables.

Roll out the pastry on a floured surface to a shape slightly larger than the top of the pie dish. Cut off a long strip of pastry all around the edge. Reserve this and other trimmings. Brush the rim of the pie dish with water, then press the narrow strip of pastry all around the rim. Brush the strip with a little more water, then place the large piece of pastry on top. Press to seal, then trim, knock up and flute the edge of the pie.

Make decorations from the trimmings, brush the undersides with water and place on top of the pie. Brush the pastry lid with a little beaten egg, and make a hole in the centre. Bake in the oven for 40-45 minutes until the pastry is golden brown and the vegetables are tender. Serve at once.