In a large saucepan, boil the potatoes in their skins for 15 to 20 minutes until soft. Drain, and cut any large potatoes in half. Allow to cool.
Heat the oil in a frying pan and add the mustard and cumin seeds, cooking until they pop. Add the carrot and cook and stir for just a few minutes. Remove the carrot and seeds from the pan and combine with the vinegar.
Combine the potatoes with the carrot and season. Mix well and serve.