For the sauce
Soak 8 bamboo skewers in cold water for at least 30 minutes. Thread the salmon and leeks alternately onto the soaked skewers. Leave in the refrigerator until needed.
To make the sauce, put all the ingredients in a small saucepan, and heat gently over a low heat, stirring, until the sugar dissolves. Bring to the boil, then reduce the heat and simmer for 2 minutes. Strain the sauce and leave to cool. Pour about one-third of the sauce into a small dish.
Heat a barbecue or grill until medium-hot. Brush plenty of the remaining sauce over the kebabs, and cook for 10 minutes, basting frequently with the sauce. Serve hot with the reserved sauce for dipping.