No longer the financial centre (4)

I believe the answer is:

then

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'no longer' is the definition.
Both the definition and answer are adverbs. Perhaps they are linked in a way I don't understand?

'the financial centre' is the wordplay.
'centre' says to take the centre.
The central letter of 'financial' is 'n'.
'the'+'n'='THEN'

Can you help me to learn more?

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

I've seen this clue in the Evening Standard.

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