For marinade mix well oil, vinegar and mustard. Spice with salt and pepper.
Peel and quarter eggs. Quarter tomatoes too. Wash leeks, remove dark green end and cut widthways into 5 mm slices. Bring water to the boil and blanch leeks about 2 minutes. Douse with cold water and drain well. Cut ham into slices und combine with leeks. Add marinade and toss gently and divide onto plates, arranging with eggs and tomatoes and sprinkle with horse radish.