I have been having the exact same problem o2 gmail
In addition I also have a google hosted domain email address which has been affected too. This leads me to believe it is a o2/google problem.
Until now the emails have been arriving on the berry before it turns up anywhere else.
I have "fixed" it (time will tell for sure) by
deleting the account from 02email.co.uk
pushing the service books (i.e. with it no longer existing)
deleting activation messages from berry
rebooting the phone (using quickpull or battery pull)
adding the account back to o2email (whilst waiting for phone to restart
Resending service books
Seems to be okay, for now