Place all of the dried fruit in a large saucepan together with the margarine, water and condensed milk and bring to the boil
Stir frequently to avoid sticking
Simmer the mixture for exactly 3 minutes and stir occasionally
Transfer the mixture to a large mixing bowl and allow to cool for half an hour
While it's cooling, weigh the flours and sift them into a bowl together with the salt and bicarbonate of soda. (When sieving wholemeal flour, you often find small quantities of bran left in the sieve; these can be tipped on to the already sieved flour)
When the mixture has cooled stir in the flour mix and add a good round tablespoon of marmalade
Spoon the mixture into the prepared tin and bake on the centre shelf of the oven for 2½-3 hours. (Take a look at the cake about ¾ of the way through the baking time and, if the top looks a bit dark, cover it with a double square of greaseproof paper to prevent further browning)
After removing the cake from the oven, let it cool in the tin for 5 minutes before turning it out onto a wire rack
This is quite a large cake which will keep well for several weeks in an airtight tin