Wash tomatoes and apples; Quarter the tomatoes, halve the apples, remove the core and cut the fruit into small pieces. Cover and cook both in a saucepan for 30 minutes. Strain the tomato and apple mixture through a fine sieve. Bring everything to the boil with vinegar, preserving sugar, salt and chilli powder, stirring constantly. Let cook for about 3 minutes (don`t forget to stir). Stir in the finely chopped basil. Pour hot into jars and close immediately.