Combine the malt vinegar, white vinegar and sugar in a saucepan then bring almost to a boil, stirring gently to dissolve the sugar.
When almost boiling, take off the heat and stir in the dice mint.
Leave to cool, then transfer to a serving bowl, or a jar for storage in the fridge until needed.
This is a small batch that I consume quickly while storing in the fridge, however the same recipe can be multiplied and jarred for later use. If doing this follow all standard jar sterilization and preserving practices.