Do harsh littering fines lead to cleaner cities?

In the late 1960s, Gary Becker published this paper on the economics of deterrence. Expected fines induce good behavior. As I was walking in London, I saw this poster and took a picture of it. While its a pinch blurry, you should see a shoe that just stepped in someone's gum. Somebody must have thrown this gum down on the ground rather than throwing it out. The caption says; "If you're caught dropping litter you will be fined 80 pounds." Now keep in mind that the exchange rate is $1.8 per pound so this is a pretty serious penalty.

What is the probability of being detected littering? The streets of London are covered with security cameras but I don't know if anyone is monitoring them for litter bugs.
How does this "old school" punishment green London? I would posit that there will be less litter. How much less litter? It would interest me if anyone has tried to quantify this?
As we know, Singapore has been able to enact credible punishments and by raising the expected cost of malfeasance this has induced good behavior. As someone who wants to see the rise of "Green Cities", I don't care if cities use carrots or sticks as incentives to achieve these goals. From a public finance standpoint, sticks (such as littering fines) are cheaper for me than paying people to pick up litter.
How cities balance individuals' rights to privacy (ACLU stuff) versus minimizing individuals' infringement on everyone else's common property (i.e litter, public spitting, dog poop) is an interesting tradeoff we face.