"Are you from the UK?"
か is used to indicate a question is being asked! You can add か to the end of many statements to turn them into questions, which may change the implied subject of the sentence. For example, アメリカ人です。➡️ I am American. アメリカ人ですか？➡️ Are you American? By simply adding か, the subject changes from the speaker ("I") to the other person in the conversation ("you").
Japanese doesn't mark the "person" in verbs, and the subject is not given; so grammatically it would be a possibility.
However, in real it would be odd, even in English; you are supposed to know from where you are, aren't you?
As a thumb rule, if subject is not specifically given, then assume it is "you" (that is, the listener) for interrogative sentences, and "me" (that is, the speaker) otherwise.