Leaders from Tooting and Walthamstow chill now and again (5)
I believe the answer is:
twice
'again' is the definition.
(I've seen this in another clue)
'leaders from tooting and walthamstow chill' is the wordplay.
'leaders from' indicates taking the first letters.
'and' is a charade indicator (letters next to each other).
'walthamstow' becomes 'w' (this could be a standard abbreviation I've not previously seen).
'chill' becomes 'ice' (icing is a kind of chilling).
The initial letter of 'tooting' is 't'.
't'+'w'+'ice'='TWICE'
'now and' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for twice that I've seen before include "Two times" , "You only live -- (film)" , "Double in quantity" , "Doubly" .)