In a bowl, dissolve the salt in the hot water and leave to cool. Add the vegetables and soak for 24 hours, drain and rinse. Mix together the mustard, turmeric, ginger, mustard seeds, pepper, flour and sugar with half the vinegar to make a paste.
Heat the remaining vinegar in a pan, add the vegetables and simmer for 5 minutes. Stir in the spice paste and bring back to the boil to thicken the sauce. Place into jars and cover when cooled.