In a heavy saucepan, heat vinegar and sugar stirring constantly until sugar has dissolved. Add mango, onion, garlic, ginger, raisins, mustard seeds and chilli flakes; stir and boil uncovered for 45 to 60 minutes until it has a syrupy consistency.
Fill the chutney into sterile preserving jars and screw lids on tight. Place jars into a large saucepan; pour in water until you reach 2/3 height of the jars. Bring to the boil and simmer for 15 minutes. Use tongs to remove the jars from the saucepan; turn them upside down and leave to cool.