There are slight differences between the two, although you are mostly correct. ‘To clock’ in AAVE and Black LGBT+ Ballroom culture is ‘to notice something someone is trying to hide’, which came in around the 1980s. For general British slang, this started between 1910s-1930s, and means ‘to notice’ in general, not ‘notice something someone is trying to hide’. It’s commonly used, and I hear it in every day British life.
I don’t know what your culture is or your experiences are, but it is just as British as it is Black and Queer Ballroom Culture.