Put the strawberries in a large bowl with the lemon juice and basil, and set aside for at least an hour.
Place the strawberry mixture into a large preserving pan (or a very large saucepan) and cook over a low heat for 10-15 minutes until the strawberries have reduced to a soft pulp – you can add a little water if the fruit sticks to the base of the pan.
Add the sugar and stir over a low heat until it is completely dissolved. Raise the heat and bring to the boil. Cook the jam at a rapid boil, stirring occasionally to prevent the jam burning on the bottom of the pan. The jam should take 7-10 minutes to reach setting point – to test when it is ready spoon a small amount of jam on to a cold saucer. Leave for one minute and then, using the tip of your finger, push the jam and if it wrinkles then setting point has been reached. If it isn’t quite ready, continue to boil the jam and test 2 minutes later.
Towards the end of the cooking time, sterilise the jars. Preheat the oven to 120C, fan 110C. Wash and dry the jars, place them on a baking tray and heat in the oven for 10 minutes.
Pour the jam into the hot jars, add a waxed disc to each one and seal with a lid. When the jam is cold, it is ready to eat! Serve with warm scones and clotted cream.