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 then 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 then 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 then turn them upside down and leave to cool.