Combine the malt vinegar, white vinegar and sugar in a saucepan, stirring to dissolve the sugar.
When just starting to simmer, stir in the mint. Remove from heat.
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 sterilisation and preserving practices.