Do we all know? I think you might think you know, but as far as I can tell there could be a few reasons they still aren’t doing it.
A) the police don’t want the public to know about an epidemic of crime by ethnic minorities. - Unlikely, because surely it would benefit them to make it public, or at least have it factored into government policy on immigration.
B) the police are being pressured by government not to release these data. - Possible, but that would mean every government of every colour has done this for decades. Wouldn’t the Boris/Braverman era tories have benefitted from this if immigrant crime was a huge issue? Perhaps they realised the figures wouldn’t benefit them and asked to keep them quiet, who knows?
C) the police in publishing this data would face public scrutiny, from both ends of the political scale. If the figures show, for example, that a much larger number of immigrants were being stopped, searched and arrested, it would lead to further accusations of institutional racism, or “two tier policing” - This seems plausible, and further, if the number of those arrests resulting in a conviction would be liable to question too and whether it was more or less than average for the country in general, someone has questions to answer.
D) the police are aware that in publishing these data, it could lead to further unrest in the country at a time when race relations are a powder keg. Statistics will be taken by either side to support their cause, and the complexities of reporting crime (particularly in sexual assault cases), of bias in investigating and prosecuting these cases from start to finish will be ignored. - This also seems plausible. In my anecdotal experience, whenever a report is put out on SM by local police forces and the ethnicity isn’t mentioned, the comments are flooded with “doctor or engineer” or veiled racist tropes, suggesting our women and girls are not at all safe, all whilst making no mention of the victim of the crime. They are conspicuous by their absence when later in the day someone points out it was a local white man who has been arrested. I don’t think anyone can argue that any crime by and non white person is taken as an invitation to brand an entire culture in the way we don’t do with white individuals.
E) the police are just really shit at capturing data. Paperwork is filled in too quickly, never properly completed, potential out of a boredom of it, or because they have so damned much of it to do. - Knowing a few police officers and hearing their tales of paperwork woe, this is plausible too.
F) another reason I haven’t thought of, feel free to add yours.
I have no idea what the real reason is. I suspect it’s a combination of C, D & E, but until someone actually tells us, I don’t think we’ll ever know.