A common exclamation when some crockery's broken! (3)
I believe the answer is:
cor
'a common exclamation' is the definition.
The definition suggests a singular noun which matches the answer.
'some crockery's broken' is the wordplay.
'some' indicates taking the first letters.
'broken' becomes 'or' (I can't justify this - if you can you should give a lot more credence to this answer).
The initial letter of 'crockerys' is 'c'.
'c'+'or'='COR'
'when' is the link.
Can you help me to learn more?
(Other definitions for cor that I've seen before include "Surprised expression" , "Blimey" , "Expression of surprise" , "Gosh" .)