People are still stuck in the dark ages where they think racism is simply prejudice against another race. It's more complicated than that now.
Casual racism is rife. Most people don't think they're racist as they feel accepting of other races. But they don't realise how negative connotations are attached to a person's colour, and I'm going to throw nationality and religion in there too.
Basically, the test is, did the race or nationality need to be mentioned? And if it was, why was it deemed necessary?
So for example, if you're telling a story about a taxi driver who was driving badly and you said, "The taxi driver was from Eastern Europe and was a really bad driver, so I didn't feel safe."
You could ask yourself why it was necessary to mention where the driver was from. Why did you not just say "the taxi driver was a really bad driver and I didn't feel safe"?
Attaching a negative comment about driving to a being Eastern European is casual racism.
Another example, a 15 yo (white) boy is discussing whether he'll ever have kids and he says "I'll either have no kids, or loads with a black woman, there'll be no in between."
The implication being that having loads of kids with a black woman is more extreme than having loads of kids. That's casual racism.
Both examples are true stories. And it happens all the time in the UK.