Cook the asparagus in boiling salted water for 3 minutes, until just tender. Remove using a slotted spoon and plunge into iced water. Drain well and place on a board.
Remove the tips and set aside. Cut the stalks into 2.5cm/1in pieces.
Meanwhile, make a dressing. In a large mixing bowl, whisk together the mustard and lemon juice to form an emulsion. Gradually add the oil, whisking continuously.
Add the pieces of asparagus stalk and the radishes and mix until evenly coated. Add the herbs and mix again. Season with salt and pepper.
Pile the dressed asparagus stalks on a platter and scatter the reserved tips over the top. Pour over any remaining dressing.