Popular in the London area at society functions (5)

I believe the answer is:

sines

'functions' is the definition.
(sine is a kind of function)

'popular in the london area at society' is the wordplay.
'popular' becomes 'in'.
'in the' is an insertion indicator.
'london area' becomes 'se' (abbreviation for South East).
'at' means one lot of letters go next to another.
'society' becomes 's' (common abbreviation in names of organisations).
'in' placed inside 'se' is 'sine'.
'sine'+'s'='SINES'

(Another definition for sines that I've seen is " functions".)

I've seen this clue in The Independent.

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