This red posting box dates from between 1910 and 1936. All traditional style British post boxes have the initials of the reigning monarch at the time they were erected. Thus GR here stands for George Rex i.e. George V. Discovered on a little used lane, almost but not quite in the middle of nowhere. Fascinating to think that you could post a letter there and it could end up at any recognised postal address in the world, even Buckingham Palace or the White House or a hotel of your choice in Timbuctu.