Runner bean, smoked trout & potato salad

Name: Runner bean, smoked trout & potato salad
Prep time: 15 min
Cook time: 15 min
Total time: 30 min
Cuisine: British
Ingredients: 500g new potato , scrubbed and cut in half; 300g runner bean , trimmed and sliced; 4 spring onions , sliced; ½ bunch parsley , roughly chopped; 150g pack smoked trout , flaked; 50ml extra-virgin olive oil; juice ½ lemon; 2 tbsp red wine vinegar; 2 tsp wholegrain mustard; 1 tbsp horseradish sauce