The cache is hidden at N51 48.ABC W000 35.DEF where:
Location 1 (given co-ords) - Sign W: "...when the Estate was sold in the 1XY0s..." X-Y=A
Number of letters in the word describing the Fallow Deer which are frequently spotted in this area of woodland = B.
Location 2 - Sign E - 48.767 35.427: "If you visited Ashridge during the Victorian period you might have found [number of letters in word MINUS TWO = C] roaming the woods..."
HALF the number of letters in the word before Lodge = D.
Location 3 - Sign Y - 48.733 35.484: "The bank marks the boundary between Pitstone Common and Shallow Copse, which was "enclosed" in 1ZF2.