At that time, the National Front (4)

I believe the answer is:

then

'at that time' is the definition.
('then' can be a synonym of 'at that time')

'the national front' is the wordplay.
'front' indicates taking the first letters.
The initial letter of 'national' is 'n'.
'the'+'n'='THEN'

(Other definitions for then that I've seen before include "soon?" , "Consequently" , "At that time; next" , "Subsequently - previously" , "Afterwards - as a result" .)

I've seen this clue in the Evening Standard.

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