Put the currants, sultanas, raisins, mixed peel or dried cranberries and glace cherries into a large mixing bowl. Cover with boiling water, stir well, then drain thoroughly. Return to the bowl and stir in the rum or brandy. Cover and leave for several hours, or overnight. This plumps up the fruit to make the cake deliciously moist.
In a very large mixing bowl, beat together the Trex and sugar until light and fluffy. Do this with a wooden spoon, or use a hand-held electric mixer. Gradually add the beaten eggs.
Sift the flour, salt and spices into the mixing bowl, folding them in with a large metal spoon. Add the fruit mixture and stir in thoroughly. Tip the mixture into the prepared tin, levelling the surface.
Stand the cake on a wire rack and leave it to cool in the tin. When completely cold, wrap in greaseproof paper and store in an airtight tin. About 1 week before Christmas, coat the cake with almond paste or marzipan, allowing it to harden for 24 hours before decorating with royal icing.