Meanwhile, in a large bowl, combine flour, currants, sultanas, suet, breadcrumbs and sugar. Mix egg and milk with mixed spice, baking powder, salt and golden syrup. Stir into flour mixture to form a wet dough.
Dip a heavy cotton cloth (cloot) in boiling water and then sprinkle it with flour. Place dough in centre of cloth, draw opposite corners together to form a ball, leaving a bit of room for the dumpling to expand, and tie tightly.
Place the dumpling in the boiling water, reduce heat to a low boil and cook 3 1/2 hours, topping water off as needed. Remove the dumpling from the water, remove the cloth and dry the dumpling in front of a fire or in a 150 C / Gas mark 2 oven until surface is no longer wet.
If you don't have a cloot already, try using an old pillowcase, a square of muslin or a large tea towel.