GEOCACHING ON NATIONAL TRUST PROPERTY IS AT YOUR OWN RISK.
Also, please note that the National Trust is caring for the specialist habitats and landscape you enjoy on this and other caches on NT property, which is one of the reasons we are glad to be members.
All the guessing has been done now, so here is the puzzle.
The first thing you must find is at
N51 1 (V + Y).(LO + F) (X + U) (BC - T)
W000 1 (S + R).(LO + X) (V + I) (NE + Z)
At this spot you will find some writing.
A = number of letters in first line
B = number of letters in second line
C = last digit
Add A+B+C to Northing and take A*C from Westing for the final cache location.
You can check your answers for the first part here: