In Belgium, Mary was gutted, I hear, to have inferred that I'd asked her to help herself (2,2,5)
I believe the answer is:
be my guest
'gutted i hear to have inferred that i'd asked her to help herself' is the definition.
I can't judge whether this defines the answer.
'in belgium mary' is the wordplay.
I cannot really see how this works, but
'belgium' could be 'be' (I've seen this in other clues) and 'be' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'was' acts as a link.
Can you help me to learn more?
(Other definitions for be my guest that I've seen before include "Help yourself!" , "as 1 [HOTELIERS] might say" , "Go ahead" , "Do as you wish!" , "Please do!" .)