Is there anywhere else that has the US model? I worked on a UK university campus for a few years and I don't think they had any security guards (certainly I never met any and I was in and out of buildings at all hours) let alone armed police!
I think UK universities mostly include limited security in their general pastoral support, rather than having dedicated security guards. So there's someone who can e.g. ask a stranger loitering on campus at night what they're doing, but anything serious will be handled by the police.