For the pickled radishes, warm the vinegar, water and sugar in a small pan until the sugar dissolves. Place the radishes in a bowl and pour over the vinegar. Set aside for 10 mins, cover and chill for up to 24 hours.
Bring a pan of water to the boil, add the potatoes and cook for around 10 mins until just tender. Drain and rinse with cold water to stop them cooking further.
Combine all the dressing ingredients, adding enough water to just slacken the mixture.
Thread the potatoes, mushrooms, courgettes and radish halves onto the skewers, and brush with the oil.
Heat a griddle pan and cook the skewers in batches for 2-3 mins until the mushrooms have softened. Brush over the dressing and cook for another minute until beginning to char.
Sprinkle with the seaweed and serve with the pickled radishes and any remaining dressing.
Recipe by appetite magazine at https://www.appetitemag.co.uk/jersey-royal-and-mushroom-skewers/