Thoroughly mix the flour and suet. Slowly add the milk and water and mix into a dough. Set aside a quarter of it and roll out the rest in a circle. Line a 1.5-litre/2½-pint/l ½-quart pudding basin/steaming mould with the pastry and trim the edges. Chop the butter into small pieces and mix it with the sugar. Prick the lemon all over with a sharp needle, going through the skin and into the flesh. Place the lemon in the basin and cover with the butter and sugar mixture. Roll out the remaining pastry, place it on top of the basin, trim and seal the edge. Cover with greaseproof/waxed paper and foil, and tie firmly with string. Half fill a large saucepan with water, place the pudding in it so that the water comes almost to the top. Cover and leave to boil for 3 hours. As the water evaporates, top it up with boiling water. To serve, remove the foil and paper, cover with a large plate and invert to turn it out. Cut into the pudding at table and give everyone a portion of the lemon with the juices and suet crust.