Place sugar in saucepan with the freshly grated lemon zest and water. Heat slowly until sugar melts, then bring to a boil.
Shake flowers clean then add the blossoms to the saucepan, cutting off stalks close to flower heads. Push heads into liquid and bring back to boil. Cover and set aside until contents are cold.
Stir lemon juice into cooled syrup. Strain through muslin-lined sieve twice then bottle. Store in the fridge.