Erm like most of my route then !
Of the 13 miles I'd consider about 8 of them 'dodgy'. Clayton isn't the most salubrious places. I have a couple of dodgy canal bridges, especially those next to a lock, and in summer there is usually a few guys smoking and drinking under them - I generally go through at a rate of knots. (I appreciate where you are coming from having been attacked on a canal).
We've also a fairly good 'old railway' that runs east/west, about 3-4 miles south of the city, which must stretch 10 miles. It's a bit like the M1 for bikes and pedestrians, called The Fallowfield Loop. It's also got a reputation for muggings despite the relatively high traffic, and even at rush hour, or middle of the day. I've had a colleague nearly jumped, but they just clipped his head as they tried to punch him off his bike - he stopped and was about to give chase, then 'thought about it'.
Cycling in London is far safer then in other big cities, say Manchester. whilst Manchester centre is OK if busy, the main commute roads in and out are pretty bad as we just don't have a critical mass of cyclists so you get 'overlooked'. I've had too many accidents on commuting routes caused by driver's poor attention. You aren't even safe on the cycle lanes as these are generally ignored by drivers as the roads aren't wide enough.