MOR: Mandatory Occurence Report
Filed by ATC or Aircrew when certain events occur. They range from an aircraft accident to a level bust to a loss of separation to an airspace infringement to a burst tyre on landing (and many other events).
In some cases you HAVE to file one (eg aircraft accident), and in some cases there is discretion involved. For example, if someone strays into the edge of your zone but doesn't cause a major upset to other traffic, you might decide that a short chat on the R/T or a request to phone in for a 'debrief' after landing will suffice. If you have had to take avoiding action on him with other traffic, then an MOR will probably be required.
I don't know the details of this event, but I imagine that if Solent had a stream of people on incorrect tracks or infringing the airspace or whatever, they might feel that MOR was the only way to ensure the problems were not repeated.
MORs should not be seen a method of punishment, but unfortunately some people seem to use them for that.