Norfolk County Council offer Public Rights of Way data on this page :- http://maps.norfolk.gov.uk/inspire/
It is issued under Open Government Licence :- http://www.nationalarchives.gov.uk/doc/open-government-licence/version/2/
These open licence terms are all very confusing (open not always meaning open). Therefore my question is, can I copy the RoW lines from the WMS maps (which open in JOSM) and use the data in OSM?
Yes, you are allowed to ‘copy, publish, distribute and transmit the Information’.
However, make sure in the source tag you ‘acknowledge the source of the Information in your product or application by including or linking to any attribution statement specified by the Information Provider(s)’. (i.e. add something like source=“© Norfolk County Council, OGL 3.0”)