Forget back-off-envelop calculations, take official numbers. And that is 25% for London.
The calculation I made was from official figures. A smaller percentage of a larger demographic can make up a large percentage of the total.
Even if you want to ignore every number except your 25%, those white victims of racially motivated hate crimes presumably exist, do they not?
Not some calculation I cannot follw. Not press reports. And unless you go and read the official report (there is even a spreadsheet, so you can use prime sources directly), I gonna stop now.