Fawlty performed mostly somewhere in Essex (8)
I believe the answer is:
basildon
'somewhere in essex' is the definition.
The definition suggests a singular noun which matches the answer.
'fawlty performed mostly' is the wordplay.
'fawlty' becomes 'Basil' (Basil Fawlty of the sitcom Fawlty Towers).
'performed' becomes 'done' (done can mean performed or accomplished).
'mostly' means to remove the last letter (most but not all of the word).
'done' with its final letter taken away is 'don'.
'basil'+'don'='BASILDON'
Can you help me to learn more?
(Other definitions for basildon that I've seen before include "Essex new town" , "S East town" .)