There has always been two distinct dialects, one from north of the Thames and another from the south. Having been brought up in a family that were north and then moved south it became apparent that there were sometimes two phrases for the same thing or two similar phrases that meant different things.
Jonathon green's Book Cassell's Rhyming Slang (isbn 0 304 35513 5)
might help, I believe it also has references to more modern additions to the langauge. Not to teach granny how to suck eggs but it was developed so that the police (who were drafted in from the home counties, because locals didn't want the job) were unaware of what was being said right in front of them. To shorten it to the first word served to make it even more confusing. As for songs if you search for music hall songs I'm sure you should find some with references. Wotcha me old brown Son metions "come and have a tiddly at the old brown bear. Tiddly wink being drink so you get a bit tiddly.
Hope some of this helps.

Ob