Wash the cherries and remove the stalks, then cut each cherry in half and remove the stones.
Tip the cherries into a mixing bowl with the sugar and lemon juice. Stir well then cover and set aside for at least 1 hour until the sugar has dissolved and the juices have started to run.
Stir again, then cover and chill for 24 hours. Add the vinegar, stir well, cover and return to the fridge for a further 24 hours, stirring again twice during this period.
Pass through a sieve into a bowl and set aside for 2 hours to ensure that all the liquid drips through . Reserve the cherries for use as suggested above.
Pass the liquid through clean muslin before decanting into sterilised bottles. Store in the fridge for up to a week.