Staffless Libraries

A wheeze that seems to appeal to Library managers trying to avoid closing buildings rather than keeping library services is the staffless library.  An example has now been the subject of a complaint in Barnet. 

Staffless libraries seem generally to work by allowing access to people with library cards and pins (i.e. existing users), but excluding children.  I don't know how places like Barnet cope with the public safety implications of having an otherwise empty building without staff.  What do they do about vandalism or drug users or possible attacks/inappropriate behaviour by users?

Given the disproportionate impact on children this may indeed be a challengable policy.