Put the raisins, sultanas, cherries and rum together in a large bowl, cover with cling and leave to soak overnight so that the berries are all plump and juicy before cooking. Heat the milk up to warm enough so you can still put your finger in it, sprinkle over the yeast and 1 tbsp sugar, whisk together and leave for 10 minutes or until it starts to turn frothy. Sift the flour into a large bowl, add the rest of the sugar, salt, mixed spice and orange zest and ground almonds and then gradually pour in the warm frothy yeast mix. Beat in the eggs with a wooden spoon and then the softened butter and stir until it comes together as a soft dough. Turn out onto a lightly floured surface and knead for 5 minutes or until no longer sticky and smooth to touch. The dough will be quite soft but not too sticky. Add a little more flour as necessary. Drain the soaked fruit and discard any remaining liquid. Mix the soaked fruit with the mixed peel together in a small bowl and then add this to the dough a little at a time by kneading it in until all the fruit has been incorporated. Return the dough to a lightly oiled bowl, cover loosely with oiled cling film and leave to rise in a warm place for 1 hour or until it has doubled in size. Preheat the oven to 160°C. Line a baking sheet with nonstick baking paper. Roll the dough out to make a rectangle approx. 30 x 25cm. Shape the marzipan into one long sausage approx. 2cm in diameter just slightly shorter than the length of the dough. Place in the middle of the dough and then wrap the dough around it and seal tightly at the seam. Turn over so that the seam is on the underside. Transfer to the lined baking sheet and leave to prove again for 30 mins - 1 hour or until it has doubled in size. Transfer to the preheated oven and bake for 45-50 minutes or until it is well risen and golden brown all over. Cool on a wire rack, dust well with icing sugar and serve in thick slices with a hot cup of tea.