Don't get confused between "IRIS" and Facial Recognition "E-Gates". I think MAN has both - although not in every terminal.
As I understand it, IRIS is to be phased out (no new applications accepted I believe).
I also believe that it is UKBA who are responsible for having the machines operational and turned on/off when flights come in. I think UK Airports themselves often get a bit of grief for these machines, when they just host them.