Don't be intimidated by the fact this cache is listed as a
Mystery/Puzzle, in fact, it should make it easier to find the
cache. I was tempted to make this a regular cache, but because of
the high muggle nature of this area, I figured it would be very
difficult without a good hint. Instead, I decided to make it a fun
and (very) easy puzzle. By solving this puzzle, you should know
exactly where the cache is.
The posted coordinates will take you near a plaque. The
satellite reception is very poor in here so the coords will take
somewhere near the plaque. You should be able to easily find it.
This is the plaque you are looking for:
When you find the plaque you need to add the first and last
digit of the last year Mr. Menzies served as an Alderman.
Now look to your left. Use this number to count the large
metallic blue post holding the rail. The cache is right under that
post.
I hope this makes it easier. Please use your extreme stealth
ability and be careful of muggles as there could be many in the
area. You may have to come back another time if you come at a high
muggle time. Night time should work good for this cache (for all my
night caching loving friends! 
)
Happy caching!