Big British salad

Name: Big British salad
Prep time: 10 min
Cook time: 15 min
Total time: 25 min
Cuisine: British, European, World Cuisine
Ingredients: mini new potatoes; fine asparagus; white wine vinegar; lemon juice; Fairtrade caster sugar; sunflower oil; mustard powder; large red onion, finely sliced; cucumber, washed, halved and thinly sliced; radishes, washed, trimmed and thinly sliced; washed and chopped fresh flat-leaf parsley; watercress, washed; smoked mackerel, skin removed, and flaked into pieces