Upon what basis can an Occupy protest ask someone to leave?

Upon what basis can an Occupy protest ask someone to leave?

via Samizdata.net by (Natalie Solent (Essex)) on 11/23/11

... because "This is private property" or any other version of "You have no right to be here" are open to some fairly obvious ripostes.
"We were here first" - "Er, not quite first. The actual owners of the space were there before you."
"We are the 99%" - "We're poorer than you, you middle class ****-ers"
"We represent the 99%" - "Who voted for you, then?"
"We are the official accredited Occupiers" - "We refuse to be defined by your oppressive structures, and hereby declare ourselves to be Occupying this Occupation!"
I have been reading the minutes of the General Assembly of the Occupy protesters who have taken over the empty UBS bank building in Sun Street, Hackney. One area of concern does seem to be people "abusing the space".

If people want to stay over night (sleep-overs) they need (1) to be part of a working group (2) They need to have an on-going task that warrants their stay. There will be 'monitors' to make sure sleep-overs are not abusing the space. Individuals that stay over and are found to not be working will be given one warning before being asked to leave.

And if they say no, what then? When a warning is given, it must be a warning of something. Presumably it is a warning that the bigger group of Occupiers will eject the smaller group of Occupiers - because they can.
Unless, of course, they can't. If a fight develops, what then? Call the cops? Problem with that.