Just a couple of points to add in response to some of what I have been reading.
1. If MAN has a 'No Diversions' NOTAM in force then no flight would be filing MAN as an Alternate and hence not holding overhead whilst trying to find another airport willing to take them, as one poster suggested earlier. If the situation became an emergency then MAN has stated that it will accept them.
2. If ground handling is the issue then the airlines (AOC) will need to investigate and take action, as it is the airlines, and not the airport operator MAG, who let the handling contracts. One would assume that these contracts have some provision for handling diverted flights. I feel certain that MAG will have consulted with the AOC on this issue.