Boris's once sober occasion? (12,5)
I believe the answer is:
conservative party
'boris's' is the definition.
Both the answer and definition are singular nouns.
Perhaps they are linked in a way I don't understand?
'sober occasion?' is the wordplay.
I cannot quite understand how this works, but
'occasion?' could be 'party' (party is a kind of occasion) and 'party' is present in the answer.
The remaining letters 'conservative' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'once' is the link.
Can you help me to learn more?
(Other definitions for conservative party that I've seen before include "political group" , "the blues" .)