Put the Worcester sauce with the chopped onions in a pot and simmer gently with the brown sugar.
Add the remaining ingredients and simmer for 30 minutes, stirring continuously. If necessary, add oil if it thickens too much.
The sauce will keep well sealed in the refrigerator for several weeks. Tastes great with grilled meat, sausages etc. Can also be used on bread, e.g. on cold cuts.