The cache is in Bletchley Park proper, so you will need to pay for entry to find this one. Please do not ask for free entry, the park is operated as a charity, and needs your donations.
Bletchley Park is just south of Milton Keynes. It's quite hard to find, so it's worth printing a map from the web site - Bletchley Park. Details of current admission fees can be found on their website. Bletchley Park is a fascinating place, well worth a trip. You can see the first ever electronic computer in the world (Colossus) - I'm assured it beats America's ENIAC! You can also see a real Enigma machine, visit a computer museum and more.
This was originally a multi-cache, consisting of three clues, and a final cache location. However, there is now only one clue, but it has been relocated OUTSIDE the park, so there is no need to pay to get the clue. The GPS location given in this posting as the location of the cache is the one that used to be the location of the first clue, but now it serves only to locate the cache in roughly the right area on the map. It may also save you from the horrors of getting lost in Milton Keynes (Hint: The park entrance is very near to Bletchley Railway Station.)
It is completely possible to find the final cache (which in INSIDE the park) without the use of the clue.
To find the cache, "all" you need to do is to de-crypt this cyphertext.
TSEPT WYMVY NZWUB XUMAU UESVW YFCEU FQIPX QZVQU
WDTBI YEBRX TSEFB NVBUX OFGUM BVUNO NRAGX UELCG
RVAAW JRGSU RPNGK SRAAU RXAYL NFXFZ ACTNM NYMFU
UEHRK HVLTK OQTUX PZAVZ OCCRG NIMJO TSACH MKJBD
OYTUX IKPRX STDRH ZKPRL EYCRL NFXJG LVTBM BVERY
TLLBG AKPRX OLDVG NYMTK NPRNE XZZRI TTOAH ZKPRS
AYSVH HJBBV YZUCT MJIPG RAAED IEGBA RWESM MKWCV
ADSJX UCABY ECVRW IEGBA RCITA NJBBV PLSFT HVUCZ
YMIPR WCMFN EOOAR ILZEO GSTGA YCIXK IDTBR ILZYK
FEAGM BZACU IYTFM IGENR KQOEP UILNR IETYX QRGGU
TSEJA CKMOU LWAEW MFVLU UCRVZ BKEUK RPTUX LVQFG
GCAFL SRZRG BPHVG XKPRY EMOYE UILFY TZPGN LEZVM
HEIAM IKPRM RLSFR UIMNY TZPCT MKBUK BCOJG ZZZRK
XTTQH IIWAE OFREB AYBNT DEHRV UTPRO SSIQW YECAJ
ECTUX VLAUZ HLTVL HFEVT FCOAM IWGBA SEOCM BVWEO
GTNNE BZLVT GWOPT NZWAN ADBRX HUMPO MLTRW VPONX
DPNRK MSCGZ HPGEX YEKNI HPIFA CULRT IYPYT CEAVM
For fans of crypto type caches, take a look at
Or a little further afield, and a lot more fiendish:
Scholar Godsend, confused. (7,7) (Bucks)
Who Will Save The Sane? (Bucks)
The Lecture: Lesson 6 - Latin 1 (Herts)
Bonus: All In Order (Bucks)