The cache is located at the centroid of these three coordinates.
River Misbourne island: 51 40.371 N, 0 38.179 W
St Leonard's Church grounds: 51 41.510 N, 0 36.265 W
Bendrose Farm field: 51 39.956 N, 0 34.985 W
Note that there is no need to physically visit these locations.
The cache location itself can be very muggle dense: you'll need to be reasonably surreptitious with the cache to avoid attracting undesired curiosity. There's room in the container for a couple of small swappables - I've started it with a pack of cards.
You can check your answer on GeoChecker.com - this checker accepts answers up to 8m from the actual spot, in case there are any rounding errors in your calculations. This should be sufficient to get you to the cache site.
You may find it useful to be a moderately tall person, or have one with you, when you go to get the cache.
Well done to Smokeypugs for another speedy FTF.