Not big, not clever

"It's not big and it's not clever" seems to be a British catchphrase. I'm American, and we don't see it on native soil over here. What's the origin?

I don't know the origin, but it is a stock phrase used in UK dramas where a teacher is telling off a wayward child for 'acting big'.

I sense an opportunity for an old joke here. Did this one ever reach the US?

Inflatable teacher to inflatable child in inflatable school:

"You've let me down, you've let yourself down and, worst of all, you've let the whole school down."