The cult science fiction series Dr Who featured a travelling device known as a TARDIS. It should have had a "chameleon circuit" to make it blend into its environment. Unfortunately, the Doctor's was stuck in the shape of a 1960's "single" British police call box. Fortunately, when the show started, they were common all over the UK, so the disguise was at least plausible. Unfortunately, that is no longer the case.
To log this cache, you'll need a photograph of yourself by one corner of the TARDIS. Since it can travel in time as well as space, you'll need evidence of the date you log the cache as well as the location (for instance, including a newspaper in your photo). Stripy scarf is optional.
Note that this cache is for the SINGLE BLUE call boxes only (with a square footprint). The commoner DOUBLE ones (with a rectangular footprint) don't count. Nor do red British phone boxes. Take your photo from the corner to prove it's a single.
The usual locationless cache rules apply - one "find" per geocacher, each location can be logged only once.