2) In a small saucepan over a medium heat, combine the white vinegar, sugar, allspice and the remaining salt. Stir well until the liquid is simmering and the sugar has completely dissolved.
3) Pour the pickling liquid over the cucumber and red onion and stir to ensure everything is evenly coated. Allow to cool to room temperature, then cover with cling film (press the cling film down onto the top of the liquid so there is no air) and refrigerate. Chill for at least 4 hours to cool completely before serving.