Hooked on Caching (UK) Mystery Cache

Not at the above coordinates, which are those of Guildford and Godalming Croquet Club.

I'm a very new geocacher, but it's fair to say that I've become hooked on caching, hence the title (NB I subsequently discovered that 10 caches in the USA have the same, or similar, title, so I added the (UK), which is of no significance whatsoever). This is my first attempt at a puzzle cache. I hope it will, albeit briefly, amuse/entertain/frustrate those of you for whom the puzzle cache is the only type worth doing. Note that the cache is probably best approached from the north west.

The cache is at

N51 11.X
W000 38.Y

where
X = (T x T x T x V) + U + S
Y = (T x V) x (T + S + U) - V - S - U

The fishing rights to this stretch of river are owned by Godalming Angling Society.