(Photos copyright and licensed for use under Creative Commons, non-commerical, share-alike.)
While the first police to turn up instructed that it was a civil mater until the point of assult or obstruction, the security continued as before as soon as the police left. The second set of police to arrive took a more pragmatic approach. They said they'd do nothing until given advice from higher up and while they were there the security were forced to step back from pulling people off the fences when they climbed over.
Meanwhile, inside, kids played on a bouncy castle in the sunshine and people wandered around looking at the wide variety of art decorating the large commerical building. Workshops were also taking place around the building and there was a schedual of films and experimental performances.
Shortly before I left, higher ranking police had arrived and were expressing concern that they would be an unlicensed rave taking place in the building that evening as that's what they were being told by the security firm. The police asked if they could have a look around but after a period of discussion those inside said no.
As I left at around 6pm, the situation remained that people wanting to enter the property had to climb over a ladder tied to the fence and could do so without obstruction from either security or police. It was not clear what would happen next but the exhibition is well worth a visit.
See also http://www.taaexhibitions.org/ and http://www.randomartists.org/