The cache is not at the listed co-ordinates.
The information you need to find this cache can be found by completing the Cheltenham Racecourse Adventure Lab Caches. The difficulty and terrain rating reflects this. To find the Adventure Lab stages you will need to download the Adventure Lab app and log in using your geocaching credentials. The numbers required can be found in the journals of completed stages.
The final location can be found at:
N51 55.ABC
W002 03.DCA
The cache is a camoflaged 25ml pot.