In a large heavy bottomed saucepan, add the mustard seeds and cook until they pop. Add the grated apple, vinegar, sugar, lemon rind and bay leaves and simmer gently for about 10 minutes until soft.
Stir in all of the remaining ingredients and bring to the boil. Lower the heat and simmer gently for 30 minutes until the mixture is thickened. Remove from the heat and remove and discard the bay leaves.
While the relish is still hot, ladle into sterilised jars, seal tightly and leave undisturbed overnight to set. Store in a cool, dark place until needed.