This is British
English.
1. A "full stop" is the most common punctuation mark used at the end of a sentence and is also called a "period" in American
English.
2. After a statement with a great degree of
gravity, a brief pause followed by "full stop" is a pithy way of saying that the foregoing statement was without fine print or hedging of any kind, stating that it's undoubtedly true and universally applicable.