Sift the flour into a bowl. Add margarine to the flour, and rub in until the mixture resembles breadcrumbs. Add the water gradually and mix together
Melt the margarine in a saucepan then add the flour and cook, stirring, until sandy in colour and texture. Add the milk, whisking all the time. When the sauce has thickened, add the mustard and chopped parsley and put to one side
Lightly season the chicken and cook on a tray in the oven until just cooked, do not over colour. Dice the mushroom and lightly cook in a little oil
Add the chicken and mushrooms to the white sauce. Stir well. Pour the filling into trays
Roll out the pastry and top the pies. Crimp edges well, brush top with milk, and make a slit in the middle of the pastry to let the steam out.
Bake in the pre-heated oven for approx 30-35 minutes until golden brown.