Indeed - this goes along with other cultural values of clearing your plate and not wasting food. Some pubs offer "senior" portions for adults who don't eat much.
It is definitely rare, but not completely unheard of; more common if you're in a sitdown place that also does takeaway/delivery. I've done it a few times. One memorable incident was in Bradford where we arrived late at a curry house after interminable faffing around, were all extremely hungry, ordered more than we usually would, and halfway through the starters and giant naan realized that we'd overdone it. Think we got more than one meal out of the leftovers.
It is definitely rare, but not completely unheard of; more common if you're in a sitdown place that also does takeaway/delivery. I've done it a few times. One memorable incident was in Bradford where we arrived late at a curry house after interminable faffing around, were all extremely hungry, ordered more than we usually would, and halfway through the starters and giant naan realized that we'd overdone it. Think we got more than one meal out of the leftovers.