Ok, this film is about a cop that goes undercover in a car ringing gang, there's loads of ferraris and lambos in it! The cop ends up falling in love with the gang leaders sister or his girlfriend! And almost joins the gang himself, the cop takes this guy down in the end. I think Andy Garcia might have been in it, but I am probably wrong! I think it might have been made mid to late 80s or very early 90's.

Any ideas? The name has eluded me for ages!

Sounds just like "The Fast and the Furious"... although that wasn't released until 2001. The only 80's movie that comes close is Point Break... but it really sounds like the first movie... a trailer: YouTube - Fast And The Furious Trailer. (http://www.youtube.com/watch?v=XG82JNkknTs)

I had a funny feeling when I put the post up that someone might say fast and furious! Thank you, but its much earlier than that! Its not point break either, I think its set in New York.