You will need a Kilner-style jar, sterilised or fresh from a hot dishwasher.
Wash and trim the radishes and slice them. Rub with the salt in a bowl and leave for 5 minutes.
Squeeze out any liquid and layer them up in the jar with the ginger. Mix the vinegar, water and sugar and pour over the radishes. Put in the fridge for half an hour – or for up to a week.