Prime Minister's usual rank? (5-7)

I believe the answer is:

major-general

'rank?' is the definition.
(military rank)

'prime minister's usual' is the wordplay.
'prime minister' becomes 'major' (former prime minister John Major).
'usual' becomes 'general' (I've seen this before).
'major'+'general'='MAJOR-GENERAL'

I've seen this clue in The Telegraph.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.