Deception that Charlie Chaplin for one was engaged in? (5,8)
I believe the answer is:
funny business
'deception' is the definition.
(I've seen this before)
'charlie chaplin for one was engaged in?' is the wordplay.
I cannot really understand how this works, but
'one' could be 'un' (northern English dialect form of 'one') and 'un' is present in the answer.
'in?' could be 'in' and 'in' is located in the answer.
This may be the basis of clue (or it may be nonsense).
'that' acts as a link.
(Other definitions for funny business that I've seen before include "Dubious practice - clown's profession?" , "Underhand dealings" , "Jiggery-pokery" , "Shenanigans" , "Deceptive or disobedient behaviour (of a clown?)" .)