Mum interrupts Dad with expression of contempt (5)
I believe the answer is:
Here is my best explanation:
'expression of contempt' is the definition.
(I've seen this before)
'mum interrupts dad' is the wordplay.
'mum' becomes 'sh' (I've seen this in other clues).
'interrupts' is an insertion indicator.
'dad' becomes 'paw' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'sh' inserted inside 'paw' is 'PSHAW'.
'with' is the link.
(Other definitions for pshaw that I've seen before include "Exclamation of contempt", "Expression of contempt", "Contemptuous expression", "exclamation", "scornful reaction", "Contemptuous riposte", "Contemptuous cry", "Voice impatience", "Exclamation of impatience" and "Expression of impatience".)