It is still in use, although the rhymes do change, I've heard 'Sexton' ('Sexton Blake'- the fictional detective - used for both 'cake' and 'fake', depending on the user); and some pass into common usage and become obscured.

How many people use phrases like "Use your loaf" without thinking Loaf-of-bread=head ?

By the bye, rhyming slang has been recorded from Australia to the West Coast of the USA (travelling the long way) so WHY does everyone insist on calling it 'Cockney' rhyming slang?

I was once slagged off by a woman at work who objected to my language (she objected to 'sexual references') because I'd used the terms 'a cock-up' (a printers' term <1>) and going 'balls-out' (an engineering term<2>) she commented that it gets on her wick' - difficult since she didn't have one (Hampton Wick = I'll let you lot supply the rhyme).

Some terms are based on an already extant slang term, the old sixpence piece was a tanner = 'tanner and skin'= a 'thin (a Victorian term for sixpence.

Walrus

<1> Cock Up - one letter in a 'movable type' bed which is higher than the rest and spoils the page.
<2> Go balls out - To go at full speed, such that the ball weights on the governor of the engine are at their maximum arc diameter and the engine is working at full capacity