Crown Copyright on Ordnance Survey maps expires 50 years after the end of the date of publication. ie: this has been out of copyright since 1st January 1974.
Licensing
This work is an Ordnance Survey map over 50 years old, which is covered by Crown Copyright which in this case expires 50 years after publication. Ordnance Survey does however ask that they be credited and that the date of publication be given. Any ancillary rights gained through the creation of the electronic version are granted as freely usable under any circumstances.