There used to be a lot more of it in Norfolk (4)
I believe the answer is:
peat
'it in norfolk' is the definition.
The definition suggests a singular noun which matches the answer.
'there used to be a lot more' is the wordplay.
'there used' becomes 'pea' (I can't explain this - if you can you should believe this answer much more).
'be a lot' means to remove the last letter (I've seen 'a lot of' mean this).
'more' is a charade indicator (letters next to each other) (some letters added to the previous ones).
'to' with its final letter taken off is 't'.
'pea'+'t'='PEAT'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for peat that I've seen before include "Fuel dug from bog" , "Turf as in bogland" , "Bog vegetable matter, turf" , "Tape (anag.)" , "Fuel from marsh" .)