Source? It doesn't seem to be true for homicide. The US white rate is consistently between 3-4 per 100k, and the UK black rate is often above 5 per 100k.
Either way, all this proves is that the UK is overall a safer country than the US. But the racial disparities within each country are remarkably similar.
It also points to the fact that a privileged (at least in regards to wealth/opportunity) race in the US commits crimes at the same or higher rate (depending on category) than an underprivileged race in the UK.
We can't remove bias and false criminalization from stats but the contrast between two sister countries is interesting nonetheless.
If the simplified overarching premise is "Blacks are uniquely criminal regardless of circumstance", why am I more likely to be a victim of criminality in a room filled with 1000 white Americans than 1000 black Brits?
Either way, all this proves is that the UK is overall a safer country than the US. But the racial disparities within each country are remarkably similar.