Cook potatoes in boiling water until tender, adding corn for final 5 mins, then drain and allow to cool a little.
For the dressing, mix the vinegar, oil, shallot, capers, basil and some seasoning.
Heat grill to high. Rub a little dressing on the salmon and cook, skinned-side down, for 7-8 mins. Slice tomatoes and place on a serving plate. Slice the potatoes, cut the corn from the cobs and arrange over the tomatoes. Top with the salmon, then drizzle over the remaining dressing.