It is easyJet policy that the Captain must not leave the Flight Deck in flight except for physical needs. I have myself, during a training flight where we had a large First Officer on the jump seat, sent him out to warn a passenger about his behaviour. I then had the passenger arrested on arrival for continuing to be a yob. In 8 years of working at easyJet that is only one of 3 passenger behaviour incidents that resulted in the police being involved - hardly a routine occurrence.