Place the blackberries in a large pot and lightly crush (I use a potato masher).
Add all the other ingredients to the pot. Stir to mix and then bring to a boil over medium high heat.
Reduce the heat to medium and cook until most of the juice has evaporated and the mixture has reduced to a thick and syrupy consistency. This can take 90-120 minutes. Stir regularly and keep an eye on it as it can easily stick to the pan if you neglect it and/or have the heat too high.
Once it has achieved your desired thickness remove it from the heat.
Pour the chutney into sterilised jars, leaving 1/2 inch of headspace and then process in a boiling water bath canner for 20 minutes.