This cache is the seventh in the 'Surrey Arts' series started by Woking Wonders to commemorate people of significance in the various arts (literary, musical, etc.) with Surrey connections. The series was inspired by the excellent 'X Marks the Spot' puzzles.
To find the cache you will first need to identify X, Y and Z. You will also need to travel around West Surrey to pick up some information.
X and Y were trained at Art Colleges in London, and later formed a productive partnership.
In the preface to a book X claimed to hardly travel north of here (i.e. the dummy co-ordinates) apart from by train.
Z would've made a good subject for the "X Marks the Spot" series were it not for the fact that he wasn't a Surrey Resident.
Z died on an island quite a bit south of here.
Question 1: When was Z's last official birthday?
Answer: ab-cd-efgh (DMY format)
Z was a good friend of X's brother and he used their name in a strange "double-act".
With an additional step you can find the other half of that double-act within 2 miles of where X lived. Go there and you will find a red phone box near the crossroads.
Question 2: What is the phone number?
Go to where Y lived. On the green you will find a sign commemorating Bill.
Question 3: What are his dates?
You will find the cache at:
N51 (e) (m-c). (h+k) (r-a) (t)
W000 (s) (l). (n-d) (g+q-u) (v+j)