ACS1986
Thanks for the reply Chilly. I don't know the area so can't make the changes myself. I was bringing it to the attention of local mappers.
 
I'm aware of the designation tag (though personally because of its definition I'd generally only use highway=bridleway where I knew it to be a designated bridleway.) Note that popular usage prefers designation=public_bridleway (or designation=permissive_bridleway) rather than designation=bridleway