Stand the tin on a double layer of newspaper in the oven - if you have a gas oven ensure the paper is well away from the any flame - and bake for 4½ hours. If the cake is browning too rapidly, cover the tin with a double layer of greaseproof or parchment paper after 2½ hours. During the cooking time avoid opening the oven door too often as this may cause the cake to collapse.
After 4 ½ hours check the cake is cooked. The cake should be nicely risen and a deep brown all over. Insert a skewer or fine knife into the centre of the cake. If there is sticky dough on the skewer when you pull it out it needs cooking longer, if it is clean, the cake's done so remove from the oven.