I have asked my Employer why we don't have BOH as a diversion especially for LHR/BRS/CWL flights and have been told that the airport cannot guarantee handling/passengers services and that any diversions would be on a first come first served.
So for all these flights out no1 is BHX, although if I am operating I would always give BOH a try as I could be home in 5 minutes
http://images.ibsrv.net/ibsrv/res/sr...ies/thumbs.gif