Hi,
The campsite feature did not have any address data originally:
https://www.openstreetmap.org/way/1316595584

As a volunteer, I've added the information you've kindly given in the hope it may help your guests.
https://www.openstreetmap.org/changeset/177614321

Rural postcodes are often larger than you expect (many were created around a 1950's GPO van route!). 
Google Maps is particularly bad at routing to the mathematical centre of a large postcode area, so a link like geo:55.142438,-1.721699 is better.

For more information:
https://switch2osm.org/

Happy Mapping,

James