The cache is a short distance from the Fine Pair.
To find the co-ordinates, check the following:
The Post Box No = SLa bc
The final co-ordinates are
N51 30.(c-b) b ((b+c)-a)
W000 39.((c-b)+a) b (c-(b-a))
The Fine Pair series was originally started by wizardsmum.
If anybody would like to place 'A Fine Pair' of their own please do, I would just ask that you let mattd2k at firstname.lastname@example.org know first so he can keep track of the numbers and names to avoid duplication.
He also keeps a public Bookmark List of this series so once your cache is published please contact him via his profile page to have yours added.