Re: British "Street Talk"
m5000, welcome to Using English.
I urge you NOT to try to emulate slang in your speech, regardless of which side of the ocean you are on. Slang changes so fast, and it often so limited to particular groups that you will almost certainly sound foolish some of the time, and are likely to sound foolish a lot of of the time.
A frequent "joke" on American television comedies is the dad or mom who tries to sound "cool" by using their children's slang. Either its use fits them so badly that they are absurd, or they are using outdated slang and it's even worse.
It's fine to learn it so you understand what is said to you, but please don't try to answer back in kind.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.