Sterilize preserving jars in the oven at 140C/gas mark 1 for ten minutes (lids separate).

Place a saucer in the refrigerator.

Combine sugar and vinegar in a heavy-based saucepan.

Cook over medium heat until sugar dissolves.

Add chopped tomatoes, chillies, and garlic to the saucepan.

Stir the vegetables and sugar mixture together.

Bring the mixture to a vigorous boil, stirring continuously.

Continue boiling until the setting point is reached, approximately 15 minutes.

Check for setting point by placing a teaspoonful of jam on the chilled saucer.

If the jam holds its shape when cooled, it is ready.

If not, boil for a few more minutes and check again.

Stir in the chopped oregano and season to taste with salt and pepper.

Transfer the hot jam into the warm, sterilized jars.

Seal the jars with lids, covering each lid with waxed paper.

Allow the jars to cool completely.

Store in a cool, dark cupboard for up to three months.

Refrigerate after opening.