First off, I am a mapper not a lawyer. NOT a Lawyer, got that ?
Copyright law varies greatly around the world according to local legal jurisdictions but there are some constants; ask before incorporating somebody else's work.
dofishman is right to say that O maps are works of art. A mapper might choose to draw a map the 19th century way by banging a datum pole into the ground and hand measuring everything from that point; in that case the copyright work in the map would all be that of the mapper/artist. In order to vastly speed things up, modern mappers tend to use layers of digital information obtained as the result of somebody else's work. The sources of this information might be some local government LIDAR agency, Open Street Map, Google Earth Pro, and similar. Organisations such those I have listed tend to have clear copyright statements; Google Earth's can be found here
https://about.google/brand-resource-center/product... and OSM here
https://www.openstreetmap.org/copyright . Most online LIDAR sources will have a copyright policy displayed on their website somewhere, or bundled in the zip file download, and if they don't it might be a good idea to email them and ask before publishing anything based on their stuff.
Before commissioning a new map from either an amateur or professional mapper make it really clear where you expect the final copyright to reside. The mapper can confer copyright on the club. An amateur might to do that happily, the professional will want a reasonable payment to give up copyright. Agree that before any work is done.
A club map with several sources of information on it might carry a statement like;
"This map is copyright property of CLUB NAME.
The map was surveyed and drawn by Mrs Madeupname.
The map contains data derived from;
Fictional County LIDAR,
© OpenStreetMap contributors,
Google Earth Pro.
This map is for non-profit sporting and educational use only.
This map is not for resale.
Possession of this map does not confer any access rights
to the area described.
First surveyed in 1846, latest update Spring 2350".
It might be increasingly worth while for O clubs to encourage amateur mappers to contribute to their local effort. Using freeware makes that a lot more feasible nowadays.
Did I mention that I am not a lawyer ?