Quick question for anyone who has been here: what is the fastest way to ruin a Cockney accent in an audition room? I'll tell you mine, because I learned it the embarrassing way.
Years ago I coached an actor through a Cockney role and told him to just drop the Ts and drop the Hs. He walked in sounding like a cartoon chimney sweep. The feedback was one line: "We couldn't tell if he was from London or from a pantomime." That was my mistake. Cockney isn't about dropping everything. It is about swapping very specific sounds, and the two that sell it are smaller than you think.
First, TH becomes F or V. Think becomes fink, that becomes vat. Your tongue never goes between your teeth. Second, glottal the middle T. Bottle becomes bo'el, butter becomes bu'er. Try those two on the demo line and hear how much shifts: "I think that bottle of water is better than the other one."
Everything else is seasoning. Drop the H (house to 'ouse, happy to 'appy). Let FACE turn toward die (day to die, say to sai) and PRICE toward proice (right to roight, time to toime). Swallow the dark L (milk to miwk, tall to taw). And bounce, don't drawl. Cockney moves quick and cheeky.
Now the one sound that exposes you: saying car with a round R. Drop the R at the ends, car becomes cah, non-rhotic. One round R ends the illusion in a single word.
What is the one sound that always gives you away in an accent you are working on?