The cache is not at the above coordinates; this is for a nearby rail station.
Each cache as well as containing a clue to the ENDGAME cache also contains a clue to the next cache in the “Mists of Time” series.
This first cache is a single stage and should be straightforward.
Assume 51N 1x.xxx 00W0y.yyy
Decode the following:
N.2B(B+I)2B I+N.M(B+I)(N+P)
Subtract 0.024 from your westing as cache needed to be relocated
You can check your answer for this puzzle on Geochecker.com.