The cache is not at the posted coordinates. Instead you need to read the following information about Challenge Caches to work out where the cache is hidden.
I have had a good year for Challenge Caches so far. This type of Mystery Cache requires the user to qualify for a particular challenge before they can log a Find. This is a good way of scoring decent DT ratings, though a full DT Grid still takes a while to bag: I slaved away at plenty of puzzles as well as Challenges before I completed mine. Those commenced quite easy thanks to a puzzle near Abergavenny focussed on Pi - rellies with maths skills helping with that solve - a Greek Gods one set appropriately enough by a CO named Apollo, and one based on trainers/sneakers called ‘Dunlop’. The trouble is that D4.5 and D5 puzzles really are much more difficult than those ones, so having an alternative option for them is useful. Luckily there are plenty of varied Challenge Caches around the country (and abroad), ranging from easy ones requiring a few Church Micros, to tricky Attribute combinations, to spelling ones. I still haven’t met Zeler’s Challenge of spelling his name palindromically using the first letter of T5 caches: D1/T5 Z..., D2/T5 E... etc ending with D5/T5 Z...!
Challenge Caches help guide you to interesting caches and interesting places, and I often use them to plan my trips. Finishing my Mystery DT for a Challenge Cache signed in Staffordshire required a trip to Continental Europe for D1/T5 and D2/T5 Mysteries. On the same trip I visited some of the Challenges of Marco, which involved roped tree climbing, and some set by CO Michel in western Belgium which required logging EarthCaches in multiple countries. The bird-based Die Falken Challenge in Nordrhein Westfalen was right up my street! Prior to that I had a session focussed on bagging some Little Bridges, to need just one more to complete a Challenge Cache in South Gloucestershire - that one will fall soon! There are also two cracking Attribute Challenge Series close to Bristol that I have been working towards. To qualify for the hardest of them, 100 Recommended At Night, you really need to be on fire. Stone (GC9MJHJ), one of my caches situated conveniently close to this Mystery, will add one to that Attribute tally.
Label your answers A to K then use this formula to work out the coordinates.
N 51° 48.(A-J)(F-B)(I-D)' W 2° 43.(C/J)(G-D)(D+E+G)'