About a day before you make the mix, cut a slit along one side of the vanilla pod and then scrape the seeds into the milk. Leave to steep overnight.
Put the jam jars in the freezer about 4 hours ahead of freezing the ice cream.
Whisk the eggs and sugar and stir in the cream.
Add milk and mix well.
Crank the ice cream until it's fairly firm.
Put a large ceramic or metal bowl into a larger bowl filled with ice, salt and water. Make sure you can handle the inner bowl without causing salt water from the outer bowl to spill in. This is going to be where you ripple in the jam, so you want to ensure the bowl is super cold - otherwise the ice cream will melt.
Transfer the freshly frozen ice cream into the chilled bowl (it should be the consistency of soft-serve).
Spoon in the semi-frozen jam and ripple it into the vanilla ice cream. Don't stir too much or it will all blend together and not have ripples.
Transfer the ice cream to the freezer to let it firm up before serving.
When you serve, use the food colouring to draw a Union Jack on top of each bowl. Your guests will be disturbed by your nationalism, but at least the ice cream will be delicious.
Put a used vanilla pod or two into a sealed jar of sugar. After a few days, the sugar will taste more like vanilla. I always keep a jar or two of sugar with vanilla pods, and I use vanilla sugar in most of my ice creams.