And now there's proof. OIA user Mark Hanna gathered data on timeliness from his requests on FYI. Sadly, the results confirm widespread misbehaviour by agencies:

That spike at close-of-business on the due date is telling. Some agencies at least really are dragging things out as long as possible, leaving it till the last possible minute to respond. This violates both the purpose of the Act, and the letter of the law.
This is a small data-set, but it clearly points to a problem. The good news is that FYI's database of more than 6000 requests is public, which means we can use it to get some serious data on this. This will both tell us how widespread the problem is, and which agencies are in need of a visit by the Ombudsman with fire and sword.