Trespass is a civil wrong and the police only have powers to remove trespassers in limited circumstances. For example, if 2 or more persons are present on the land and residing there for any period, and any of those persons has caused damage to the land or to the property on the land or used threatening, abusive or insulting words or behaviour towards the occupier or someone connected with the occupier.
Another example is if those persons have 6 or more vehicles on the land. In such cases the police do have powers to direct the trespassers to leave.
Failure to leave when directed to do so by the police will amount to a criminal offence.