Preheat the oven to 200ºC/fan 180ºC/gas mark 6. Unroll the pastry and cut the sheet in half lengthways, so that you have 2 rectangles.
Squeeze the sausagemeat** from the skins. Roll into 2 log shapes and place 1 lengthways down the centre of one of the pastry rectangles. Brush a little egg along one of the long edges. Roll up the pastry around the meat and seal. Repeat with the remaining sausagemeat and pastry.
Cut each sausage roll into 9 pieces and arrange on a lined baking tray, sealed-side down. Brush the tops with egg and sprinkle 6 with the sesame seeds, 6 with the poppy seeds and leave the remaining 6 plain.
Bake in the hot oven for about 25 minutes, until puffed and golden. Let cool slightly and serve with the ketchup for dipping.
** Wash hands after handling raw meat.