Although I speak British English, I do not use a lot of slang, for the reason that 1) I am not a native British person and, like I said, most slang is either regional or class related. I don't fit firmly into any British category. Secondly I am a woman and and as such I use less slang, and particularly not the type of expressions that you are after (Like in "Lock, stock....")
I am not aware of anyone who is a regular user of the forum who speaks cockney. In England, people who speak with these type of accents usually know no language other than English, so you would not find them on a language forum. One more thing; people who speak with these types of accents ALSO speak grammatically incorrect.
Basically, when you learn a foreign language, you should leave the accents, slang and swearing for LAST when you are like a native speaker.