David Gerard (fun at thingy.apana.org.au) wrote:

What counts as publication for this purpose? OS or HMSO themselves publishing them? OS licensing them to someone else who published them? Something else?

The Ordnance Survey have delegated authority from HMSO to deal with Crown copyright since they are a trading fund. However, for the purposes of Crown copyright, any authorised publication would count. The Ordnance Survey tend to publish things themselves, but if they licence someone else (like the AA for example) to publish a map based on their data, then it also counts as a publication. However, bear in mind that any non-Ordnance Survey publication will likely have a separate copyright for the publisher of the map as well.

So, any OS maps that you can buy in the maps that date from 1954 or earlier are public domain. However, copyright is not the only intellectual property to worry about here. There are trademarks to worry about. Here is a link to a PDF file on the OS website which lists their trademarks. I strongly suspect that their symbols on maps may well be trademarked as well, even if they are not registered trademarks.

So, if you can find old published OS maps from 1954 or earlier, and you're careful about trademark information, then I think you would be in the clear.