The blend varies according to the maker, but consists of various combinations of allspice, bay leaves, cardamom, cinnamon, cloves, coriander, ginger, mustard seeds or peppercorns.
No it cannot, as they are both different things. Mixed Spice it a blend of spices, (cinnamon, ginger, nutmeg, cloves, corriander seed, cassia, allspice). Allspice comes from the dried, unripe berry...