Generally speaking, UK commercials should conform to it (2,1,4)
I believe the answer is:
as a rule
'generally speaking' is the definition.
(I've seen this in another clue)
'uk commercials should conform to it' is the wordplay.
I cannot really see how this works, but
'it' could be 'sa' (old-fashioned abbreviation for sex appeal) and 'sa' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for as a rule that I've seen before include "Under normal circumstances" , "Mainly" , "In most cases" , "Generally, normally" , "26 [NORMALLY]" .)