Campaigns of British PM almost succeeded (7)
I believe the answer is:
battles
'campaigns' is the definition.
(I've seen this before)
'of british pm almost succeeded' is the wordplay.
'of british' becomes 'b' (I can't justify this - if you can you should believe this answer much more).
'pm' becomes 'attlee' (prime minister Clement Attlee).
'almost' means to remove the last letter (most of the word but not all of it).
'succeeded' becomes 's' (genealogical abbreviation).
'attlee' with its final letter taken away is 'attle'.
'b'+'attle'+'s'='BATTLES'
Can you help me to learn more?
(Other definitions for battles that I've seen before include "Fights, conflicts" , "Military set pieces" , "Military engagements" , "Campaigns" , "Lengthy conflicts" .)