Faultless service around the country is an offence! (7)
I believe the answer is:
slander
'an offence' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Maybe you can see an association between them that I don't see?
'faultless service around the country' is the wordplay.
'faultless service' becomes 'ser' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'around' means one lot of letters goes inside another.
'the country' becomes 'land' ('land' can be a synonym of 'country').
'ser' enclosing 'land' is 'SLANDER'.
'is' is the link.
Can you help me to learn more?
(Other definitions for slander that I've seen before include "False malicious spoken statement" , "Malicious gossip" , "False or malicious report" , "muckraking!" , "Snarled about malicious statement" .)