"much to my delight they were speaking broad Cockney"
Why not?
Years ago we were staying on the island of Poros on the Peloponnese in Southern Greece.
One extremely hot day when we had slogged to the top of the hill, we found a tiny shop selling ice cream.
A middle-aged woman dressed entirely in black from head to foot was tidying up behind the counter and ignored us.
When she heard us trying to interpret the ice cream packet labels in the fridge she came over and said in broad North London Haringeyese, "them're vanilla love, and those are coconut, and them are chocolate....."
Jim Carroll