[michaelt]

> If you need to take away, maybe this indicates that you're poor and need to make a meal last.

I'd say it's the other way around: The British norm of eating everything on your plate was traditionally to avoid food waste.

And even though supermarket food is incredibly cheap these days, the norm is maintained by parents who want their children to eat their vegetables.

So Brits rarely see one another asking for to-go boxes even though many restaurants will offer them for free.