Soak the mustard seeds in cold water for at least 2 hours prior to using. 

Blanch the tomatoes then roughly chop them either with or without the seeds whatever your preference. 

Peel and finely chop the onions and finely grate the ginger. 

Place the onions, the mustard seeds and the ginger in a saucepan along with the tomatoes, bring them to the boil and simmer for 20 minutes. 

Add the salt and the spices and half of the vinegar, cook gently for about 40 minutes or until quite thick. 

Add the sugar and the remaining vinegar, stir until the sugar has dissolved continue simmering for a further 10 minutes stirring occasionally. 

Allow to cool slightly, and then fill into sterilised jars, which have first been warmed then seal.