According to the Office of Public Sector Information document on copyright (http://www.opsi.gov.uk/advice/crown-copyright/copyright-guidance/copyright-in-public-records.htm) unpublished public records have had copyright claims waived allowing free reproduction, however “The reproduction of images, including copies of documents, is not covered by the waiver”

“14. The waiver of Crown copyright does not apply to Public Records which fall within the scope of Tradeable Information, which will be subject of a separate Guidance Note to be issued by HMSO. The following material falls within the scope of Tradeable Information:

unpublished records of the Ordnance Survey, the Ordnance Survey of Northern Ireland and the United Kingdom Hydrographic Office, which form the basis of maps, charts, mapping data and other related publications.
Microfilm, microfiche, digital form and photographic copies of Public Records created by Public Record Repositories but not the data which they contain.
15. The reproduction of such material may be subject to formal licensing and payment of fees.”

I would strongly recommend reading the document in full, then if you haven’t fallen asleep you could see what the National Archives have on copyright at (http://www.nationalarchives.gov.uk/legal/pdf/copyright_full.pdf).

See page 15 for the Crown Copyright flowchart of status (taking a photo created in 1944 as an example). Q.1 Was the work created before 1 August 1989 (Yes), Q.2 Is the work a photograph or engraving (Yes), Q.3 Is the work a photograph (Yes), Was the work created before 1 June 1957 (Yes), Copyright expires 50 years after creation.

The National Archive guideline seem to go again OPSI guidlines so it is anyones guess.