You can park near the listed coordinates and follow the route clockwise around all the waypoints (shown on the satellite image below) to collect the clues and solve the final location.
As the name suggests, Castlethorpe was once home to a Castle, surrounded by a large ditch and fortifications. The Castle was demolished about 800 years ago, and all that remains now are the earthworks.
I'll let you discover more about the village of Castlethorpe as you take your walk around, but will leave you with a link to a video about the place.
The cache originally contained a wind up personal radio, some headphones, a golf ball, a bouncy ball and a log book and pencil.
To calculate the final coordinates, use the following:
N52 5.B(A+D-E)(F-G)
W0 50.A(H-E)(C-D)
You're headed in the right direction once you are "up and over"!