The cache is not at the listed coordinates.
This is the seventh and last of the Harwell site puzzle cache series. The container is a small plastic box with room for very small trackables or coins.
You need a number. Let that number be ABCD.
The cache is located at N51 35.B(A-C)C W001 19.DC(C+C)
You can check your answers for this puzzle on GeoChecker.com.