I think I have already answered my own question before I ask it, but here goes:
Only the following have the Command skill: Cult leader, High Priest, Serpentman Demagogue,and the Mummy.
I am right in thinking that bigger lurkers have such large BP cost that you wouldn't be able to field that many minis for the game that you would need a figure with command (thus negating the need to activate more than one mini at a time), and
that the lurkers with command would command the big nasty lurkers to represent the fact they have summoned them and have a compel spell (well something similar as I assume the big nasty lurker wouldn't have to take a resolve test each time) cast over them when they are summoned.
I also see this a a game balance - the big nasties cost more, but would more or less be operation by themselves unless the Total BP of the Threshold player was very high.