Put the potatoes in a pan of cold salted water and bring to the boil. Simmer for 15 mins or until tender and a knife goes in easily. Drain the potatoes and return to the pan, then stand for 5-10 mins to steam-dry. Cut them into bite-sized pieces, season with salt, cover and chill until cold.
Heat the barbecue (or heat a griddle pan if cooking indoors). Halve each large chorizo lengthways and put them, cut-side down, on the barbecue (small chorizo can go on whole). Cook, turning once or twice, until they are crisp around the edges and cooked through. Slice the chorizo into pieces.
Combine the soured cream, mayonnaise and mustard, then add to the cold potatoes with the celery and dill. Gently fold the potatoes into the dressing, taking care not to break up them too much. Scatter the chorizo on top to serve.