Big Ben perhaps a mistake (7)
I believe the answer is:
clanger
'mistake' is the definition.
(I know that clanger is a type of bloomer)
'big ben perhaps a' is the wordplay.
I cannot really see how this works, but
'a' could be 'an' and 'an' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for clanger that I've seen before include "Bell possibly" , "Big blunder" , "noise that rings in the ear" , "Big mistake (when dropped)" , "Drop this to make a blunder" .)