The thing is though that the rise in multiculturalism is a long-term trend, dating back easily to the 1950s and, perhaps, accelerating lately. But the long-term trend in crime figures is downwards, or at least that's what you see in the "Crime Survery" figures over the police recording data.
Possibly the Crime Survey figures are worth paying more attention to, because while they are only estimates they are less sensitive to official reporting standards that can vary year-on-year and between police forces. Also, I'm absolutely not suggesting that multiculturalism has driven a decrease in crime. Rather, I'm saying that the picture is stupidly messy and trying to pin annual variations on any one factor, or even two, is just completely misguided.
It's also worth pointing out that there was a 26% rise in homicide figures last year, but that drops to about 7% or something of that order when you remove the 96 victims of Hillsborough, who were included in homicide official figures last year even though the actual incident was in 1989 (owing to an anomaly about how "reporting" works; the inquest verdict was returned last year).