I have had comments that balsamic vinegar is expensive to use for sauces but I pick mine up from Lidl for £1. The garlic I use is crushed so does leave little bits in the sauce but if you want it completely smooth you can use garlic granules. If you like your BBQ sauce a bit more spicy feel free to add some chili powder.
Once the sauce is made and completely cold I store it in the fridge in a washed out old ketchup bottle. It keeps for ages.
5 tablespoons worcestershire sauce
2 cloves garlic (crushed) or 1 teaspoon garlic granules
3 tablespoons balsamic vinegar
1 teaspoon dried mustard powder
1/2 teaspoon salt
1/2 teaspoon pepper
4 tablespoons granulated sweetener
Mix all the ingredients together in a saucepan and bring to a boil, Reduce heat and simmer until the sauce is thickened.