Although you can buy pickled red cabbage, it does not compare with home-made. Be sure to leave the pickle for a few days before using.
Put the cabbage, celery, green pepper and raisins in a large bowl.
Boil together the vinegar, sugar, celery seeds and mustard seeds until the sugar has completely dissolved. Pour this mixture over the cabbage, add the oil and salt and stir to combine thoroughly. Leave in the fridge to marinate for 3-4 days or at least overnight. It will keep for about a month, or longer if stored in sterilised jars.