Concealed mic at Paddington is nightmare (7)

I believe the answer is:

bugbear

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'is nightmare' is the definition.
(thesaurus)

'concealed mic at paddington' is the wordplay.
'concealed mic at' becomes 'bug' (I can't explain this - if you can you should believe this answer much more).
'paddington' becomes 'bear' (Paddington Bear is an example).
'bug'+'bear'='BUGBEAR'

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(Other definitions for bugbear that I've seen before include "pet hate" , "something really frightful" , "Cause of obsessive fear" , "One's special fear" , "A thing causing excessive anxiety" .)

I've seen this clue in The Sun.

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