As far as I'm aware as long as you have at least 250hrs P1 (gauging by your current position you are well past this point). All you have to do is sit the written exam and take a check flight.
I've heard that if you do an FAA type rating after the above 2 it can expedite the issue of the ATPL.
I know someone who has considered doing it and has gained the information from someone who has done it. Unfortunately, it does mean what I am telling you is tertiary information and probably not the best to rely upon. I'll see if I can get him to reply to this thread...
ooo, I just found this thread...
http://www.pprune.org/forums/showthread.php?t=271143