Too jolly lot? There's uproar about that (11)

I believe the answer is:

furthermore

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'too' is the definition.
(thesaurus)

'jolly lot? there's uproar about that' is the wordplay.
'jolly lot? there' becomes 'therm' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'uproar' becomes 'furore' (synonyms).
'about that' is an insertion indicator.
'therm' going into 'furore' is 'FURTHERMORE'.

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(Other definitions for furthermore that I've seen before include "as well" , "Also" , "In addition, besides" , "to boot" .)

I've seen this clue in The Times.

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