Does anyone know the origins of the expression 'urban jungle'? where it first appeared, perhaps? Hmm...

I cannot answer your specific question, but I would be pretty sure that it was pre-dated by "concrete jungle".

This is certainly the case in my coming across the two expressions. I would have been familiar with 'concrete jungle' by the early seventies and would suggest that I didn't come across 'urban jungle' until the mid/late eighties.

There was a film "The Concrete Jungle" released in 1961.