The cache is not at the published coordinates but is less than 1 mile away.
Right lets get you started…all the information you require can be found at the the start co-ords.
N51 AB.CDE W000 VW.XYZ
A = How many furlongs to Newlands?
B = How many Miles to Chesham?
CDE = How many miles to London?
V = Which George?
W = Sum of the numbers in the year it was built / 7?
X = How many flags can you see in the picture?
Y = How many miles to Uxbridge?
Z = The number of letters in the surnames of the builder + the restorer?