Since all content posted to Flickr must have a licence other than OGL3, this image, despite possibly having a non-free licence on the source page, can be assumed to be multi-licensed under the following terms:
The Open Government Licence covers most material produced under Crown Copyright by UK government agencies that have their intellectual properties managed centrally by the Controller of His Majesty’s Stationery Office (HMSO). It may also apply to works produced by other public sector bodies, if the institution in question has chosen to explicitly place them under the OGL. A number of government institutions are exempt from the central authority of the HMSO and manage their own copyrights themselves. This applies, for instance, to the Ministry of Defence, the Government Art Collection, the Ordnance Survey and some others. Works published by these bodies may not be under the OGL, unless they have been explicitly offered under its terms. [1][2]Open Government License 3OGL 3http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3true