Number of dials in central London (5)
I believe the answer is:
seven
'number of dials in central london' is the definition.
'seven' can be an answer for 'number' (seven is a kind of whole number). I'm unsure of the 'of dials in central london' bit.
'number of dials in' is the wordplay.
'number' becomes 'V' (V is an example).
'of dials' becomes 'seen' (I can't explain this - if you can you should believe this answer much more).
'in' is an insertion indicator.
'v' placed inside 'seen' is 'SEVEN'.
Can you help me to learn more?
(Other definitions for seven that I've seen before include "See 1" , "VII" , "Little friends of ..." , "Cube root of 343" , "Film" .)