Body of police that represents the Piccadilly Tube network? (4,4,4)
I believe the answer is:
thin blue line
'body of police' is the definition.
'represents the piccadilly tube network?' is the wordplay.
I cannot really understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
'tube' could be 'line' (line is a kind of tube) and 'line' is found within the answer.
This explanation may well be incorrect...
'that' acts as a link.
Can you help me to learn more?
(Other definitions for thin blue line that I've seen before include "Police holding back a riot?" , "police maintaining order?" .)