So much depends on the stress and intonation ...
He isn't a complete clown (some fraction clown)
He isn't a complete clown (not a clown, but ... er ... thanks for mentioning it, Guto
He isn't a complete clown (maybe use a different word that begins with 'c'?)
He isn't a complete clown (it's all Carrie's fault)
I think it's part of Johnson's attempt to pivot to loveable jester again. Dad tells me that today Johnson and Sunak visited his local hospital and stood in front of some radiography equipment and Johnson said "beam me up Scotty" for the cameras