BHX does have quite a few holds that it can use, and the problem of different aircraft having different minima cannot be new.Without having all of the traffic replays to hand it will be difficult to determine what the problem was but I am sure the operators will be having a talk to the atc unit at the airport to see what can be improved on. Does anybody know the maximum number of aircraft that were holding and where they were holding? Perhaps a bit of stack swapping would have helped?