Snip each sausage at one end and squeeze the sausage meat out on to a chopping board lightly dusted with flour. Roll out into thinner sausages.
Sift both flours and the salt into a bowl. Add the butter and rub it in with the fingertips until the mixture resembles fine breadcrumbs. Add enough of the measurement iced water to mix to a soft dough, then stir in the poppy seeds. Turn the dough out on to a lightly floured surface and knead briefly.
Roll the pastry out on a well-floured surface to a rectangle measuring 30 x 25 cm (12 x 10 inches), then cut into three 10 x 25 cm (4 x 10 inch) strips. Lay the sausage meat down the centre of each strip. Brush 1 edge of each strip with beaten egg, roll over and flute the edges. Cut each strip into five 5 cm (2 inch) sausage rolls and put on a baking sheet.
Make a couple of cuts in the top of each roll and brush with the remaining egg. Refrigerate for 15 minutes before baking in a preheated oven, 200°C (400°F), Gas Mark 6, for 15 minutes. Remove from the oven and leave to cool before lifting off the sheet.