Back in September Phillip Johnson commented on the UK’s economic position and the likely criminal trends in the near future:

Most violence is caused by young men against young men, usually at night, when they are drunk. At a time of economic slowdown, fewer go to pubs and clubs, there are fewer clashes and violence falls.
Domestic violence, by contrast, tends to rise as unemployed men are at home, household finances come under strain, and there is greater tension within families.

The piece speaks to the obvious fact that crime goes up as times get tough but the fact that it is crime of particular types amongst particular people speaks to how dissatisfying poverty is as a fundamental cause of criminal behavior.
My first thought: much like Venkatesh has pointed out the counter-recession aspects of the oldest profession, I would guess less money spent on state law enforcement, less money on the drug war and thus less violence in the drug war to secure rents.