The 110th in a series of caches where a red telephone box is in close proximity to a post box.
The only rule is that they have to be able to be photographed together, and the phone boxes have to be red.
To find the cache you will need to find out the phone number above www.royalmail.com on the post box. Assume these numbers are ABCDE FGHIJK.
The cache is at N 54 42.(B+C)(C+G)(D+J) W 001 35.(C+D)(E-C)(G+J)
The checksum of the 15 digits is 68