Grate the cucumbers using a coarse grater into a colander. Place a bowl underneath the colander and leave overnight to drain. It is essential to remove all the juices or the dip will be watery and separate. If you are in a hurry then place grated mixture in a kitchen cloth, pulling up the corners to make a tight bundle. Squeeze the bundle very hard to extract all the moisture.
Put grated cucumber in a mixing bowl and stir in yogurt, crushed garlic, dill, olive oil and salt and pepper. Cover bowl with cling film and chill for 3 hours for the flavours to blend. The tzatziki can be left in the refrigerator for a maximum of two days before being used. Just before serving, stir.
To serve, place three or four tbsp on a small plate or bowl.