"Trespass is not a criminal offence"
True. But aggravated trespass is. Section 68 of the Criminal Justice and Public Order Act 1994:
Offence of aggravated trespass.
(1) A person commits the offence of aggravated trespass if he trespasses on land in the open air and, in relation to any lawful activity which persons are engaging in or are about to engage in on that or adjoining land in the open air, does there anything which is intended by him to have the effect—
(a)of intimidating those persons or any of them so as to deter them or any of them from engaging in that activity,
(b)of obstructing that activity, or
(c)of disrupting that activity.
Section 69 deals with the powers of the police to deal with aggravated trespass:
Powers to remove persons committing or participating in aggravated trespass.
(1)If the senior police officer present at the scene reasonably believes—
(a)that a person is committing, has committed or intends to commit the offence of aggravated trespass on land in the open air; or
(b)that two or more persons are trespassing on land in the open air and are present there with the common purpose of intimidating persons so as to deter them from engaging in a lawful activity or of obstructing or disrupting a lawful activity,he may direct that person or (as the case may be) those persons (or any of them) to leave the land.
It goes on a bit more to say how those powers may be devolved to constables.
There is little doubt that most "traveller" incursions fall into the aggravated trespass category. There is too much pussyfooting around with them. A couple of weeks ago an area of a hospital car park was fenced off following the arrival of some of these itinerants who were visiting one of their number in the hospital. Meanwhile people who were trying to park to use the facilities were denied quite a large chunk of the car park. This was clearly a case of aggravated trespass but far from being ended by the Boys in Blue it was actually facilitated by them, no doubt under instructions from their politically correct senior officers.