Sorry, I would have thought you'd have known it is not possible to ban UK citizens from entering their own country - so I am a bit amazed that you jumped to the conclusion you did. Maybe you hit reply a bit quickly.
It is really quite simple to bar entry to people with certain stamps in their passports. It is already in place in, for example, Lebanon where you will be refused entry if you have an Israeli stamp in your passport. There used to be a similar thing for Greece, if you had a Turkish stamp in your passport you weren't allowed into Greece.