Vclaw
5
The OS OpenData is released under a free license, so it is fine to use with OpenStreetMap (though there are a few people who disagree whether it is compatible with the new contributor terms). See Ordnance Survey Opendata
Though its still a good idea to check names “on the ground” where possible to see what the street sign says. The OS data does have some errors / misspellings etc in it.
If the only source for a name is OS Locator (eg if the street sign is missing), then its helpful to tag this. eg add a tag source:name=OS_OpenData_Locator