Half of Britons wouldn't take a trip to the the moon, even in guaranteed safety

A person can be British, in which case they are a Briton

You can have a British car but only British people are Britons.

It gets more complicated in history as Britons referred to the Celtic people of Britain, as opposed to the Romans, then later the various other peoples who made up the rich tapestry of Middle Ages Britain: the Anglo-Saxons, the Vikings, etc. It's why the British Isles includes Ireland because the Insular Celts were once all Britons.

Only people are britons whilst anything can be british.