I've been in correspondence with London's Metropolitan Police] over the last few months, discussing the possibility of them open-licensing some of their images - not least the scenic (as opposed to scene-of-crime) pictures taken from their helicopters, and/ or images posted to their social media accounts.
They have decided that they so not wish to do so on a blanket basis, but say that they are willing to consider requests to do so for images in an individual basis. You may send requests to: DMC-Mailbox-.PressBureau-DMC@met.pnn.police.uk