Wash strawberries just before using so they don't absorb too much water and hull them removing stalks and leaves, half if they are large.
Warm the strawberries and sugar in a large heavy based pan over moderate heat to dissolve the sugar.
All the balsamic vinegar, lemon juice, pepper and orange zest and stir well.
Bring to the boil and boil rapidly for approximately 20 minutes or until the setting point has been reached (test with a well chjilled saucer, a spoonful should form a skin and wrinkle when you touch it after a couple of minutes).
Toss in the basil and stir well before spooning into jars.