Ross Clark says something that is easy to misinterpret. It's:
Those involved with gun crime tend to have grown up fatherless and in the absence of good male role models have gravitated towards gangs.
It would, however, be wrong to infer from this that growing up fatherless is a cause of gun crime.
Let's put some numbers on this. The Home Office reckon (ch 2 of this pdf) that firearms were used in 11084 crimes in 2005-06. Let's assume this means there are 11084 gun criminals, and let's assume all these were 16-24 year-old men.
Now, in 2005 there were roughly 3.5 million such men. How many come from single-mother households? According to table 2.6 of this big pdf, the proportion of children in single-mother households has risen from 6% in 1972 to 16% in 1992 to 21% in 2005. Taking the 1992 figure, this means there were roughly 560,000 16-24 year-old men who grew up in lone-mother households.
Even if we assume that all gun criminals come from such households, it's still the case that only 2% - 11084 out of 565,000 - of men from single-mother families become gun criminals. To get the figure this high, I've had to make some heroic assumptions.
So, at least 98% of men from single-mother households don't become gun criminals. It would be odd to say that x causes y when over 98% of xs don't cause y.
Indeed, there's a good theoretical reason why single mother households, on their own, shouldn't produce criminals. It's that the alternative to a single-mother family is not, in many cases, a family where the father is a good role model. It's one where the father is a bad role model. Removing a bad role model might be good for a child's development. Had I grown up in a two-parent household and used my dad as a role model, I'd have become a criminal.